[[caption-width-right:350: Let the hunt begin...]]

-> ''"Trust no one."''
-->-- ''The Maze of Bones'', the first book in the first series

Quiz time: What is ''The 39 Clues"?

A. Childrens' book series

B. Web site

C. Collectible card game

D. Sweepstakes

E. All of the above.

The answer is E.

The book series by Creator/RickRiordan and various other authors, as well as the website, cards, and sweepstakes, deal with the [[BigScrewedUpFamily Cahill family]], one of the most powerful families the world has ever known, as almost every historical figure from the last five hundred years is related to them. The family is divided into one of four branches - the [[TheSmartGuy Ekaterina]], who are the geniuses and inventors of the world, the [[TheBigGuy Tomas]], who are explorers and athletes, the [[BadassBureaucrat Luci]][[AmbitionIsEvil ans]], who are the spies, generals, and leaders, and the Janus, the artists, musicians, and authors.

When Grace Cahill, arguably one of the last genuinely nice Cahills, dies, she chooses to unveil her alternate will and kickstart a globe-trotting quest to find the source of the family's power. Such power can only be found by assembling all 39 Clues.

Our story begins when Amy and Dan Cahill, orphans who live with their disinterested great-aunt Beatrice, attend their grandmother Grace's funeral and the reading of her will. There, along with an assortment of colorful distant relatives, they make the choice: one million dollars or the chance to find the Clues alongside au pair Nellie Gomez. They choose to receive their first Clue, and are subsequently thrown into a five-hundred-year-old web of backstabbing, lies, and deceit. The first series follows them through the Clue hunt as they travel the globe, clash with their scheming relatives, and discover troubling truths about themselves and the Cahill family at large.

Flash forward two years to the beginning of the SequelSeries, ''Cahills vs. Vespers''. The Clue hunt has ended, but a new threat has surfaced; [[SequelHook it was revealed at the end of the first series]] that the Clue hunt was really only a practice run for a greater conflict between the Cahills and a previously unknown rival faction. This group, the Vespers, are allegedly so evil that they make the BigBad of the first series look like ''Mother Teresa'' by comparison. Now the Vespers have begun making demands of the Cahill family, and [[HostageForMacGuffin the lives of seven hostages are at stake.]] Amy and Dan are once more sent on a trip around the world, frantically chasing down Vesper One's demands, [[CombatAndSupport while their teammates provide support from the Cahill Command Center]], a computer lab that has been set up in Grace's mansion.

A third series, named Unstoppable, was published from late 2013 to 2014, dealing with some of the fallout from the conflict with the Vespers, with presidential candidate J. Rutherford Pierce serving as {{Big Bad}}. Scholastic proceeded to publish a fourth one, from early 2015 to mid 2016, in which a new villain with mysterious ties to Grace named the Outcast has taken control of much of the family's resources. A standalone novel named Outbreak was released in late 2016, dealing with the doings of a pharmaceutical company with which Sinead Starling was involved.

Here's a link to the [[http://www.the39clues.com/ the web site]]. Character sheet is [[Characters/The39Clues here]].

!!This book series provides examples of:
[[folder:Series 1: The 39 Clues]]
* AbusiveParents: This is most certainly the case with [[spoiler: Ian and Natalie]] since, [[spoiler: Isabel Kabra verbally degrades them on a regular basis. They both ''love'' her, and ''fear'' her simultaneously -- while also thinking that they lead the perfect lives because of all the wealth their family has]] They'd be [[TheWoobie Woobies]] if they weren't so nasty themselves!
* AllGirlsWantBadBoys: Amy towards Ian.
* AllThereInTheManual: Inputting cards' codes on the website either unlocks a secret file or is part of a Clue Combo. Solving website missions' and inputting ultra-rare cards' codes unlocks one of the 39 Clues.
* AmbiguouslyBrown: The Kabras.
** London does have a large population of Indian-Brits. Isabel is described as lighter-skinned than her children, so it's probably Vikram who has some Indian ancestry.
* AmbitionIsEvil: Everyone except Amy and Dan, the Lucians in particular.
* AncientConspiracy: The Cahill clan.
* ArcNumber: Despite its inclusion in the series name, 39 only shows up as the number of clues, and there doesn't seem to be any reason for it to be this particular number. (When Amy wonders about this, Dan points out that 39 is "a pretty sweet number": [[ThirteenIsUnlucky 13]]x3, the sum of the first five odd prime numbers, 3^1+3^2+3^3). (Presumably, the authors wanted a numerically interesting number that no one had used before.) 7 actually shows up more in the story (7 teams, [[spoiler: Amy and Dan discover their family branch at the end of Book 7]], and 7 captives in the sequel series. 7 is also the age Amy was when she and Dan lost their parents, and the next big change in her life comes 7 years after that, when her grandmother dies and the clue hunt begins. Then she gets a small break until she's 16, the digits of which add up to 7, when the Vespers attack.
* {{Area51}}: The Lucians are in charge of this location.
* AudioAdaptation: Read by David Pittu!
** Nellie is given a hint of accent, and the Kabras sound upper-crust snooty (which is amazing).
** Each audio book also contains a small recording at the end that reveals backstories not shown anywhere else.
* BadassDriver: While fleeing the Janus hideout, Dan becomes one of these.
** Nellie is one, too, on a regular basis.
* BadassFamily: The Cahills. Who are also a BigScrewedUpFamily, naturally.
* BeethovenWasAnAlienSpy: Beethoven certainly was, as well as Mozart, Neil Armstrong, Einstein, Churchill, Benjamin Franklin, Houdini, Bill Gates, and George Washington, among others.
* BigBad: [[spoiler: Isabel Kabra]].
* BigFancyHouse: Both Grace's house (before it burned down, although the rebuilt version also qualifies) and the Kabra mansion.
* BigScrewedUpFamily: Where do we begin?
** Basically, the majority of the LoadsAndLoadsOfCharacters are related and have tried to kill each other at some point.
* BlondeBrunetteRedhead: [[TheBigGuy Reagan and Madison Holt]] are the blondes, [[RichBitch Natalie Kabra (and her mother Isabel)]] are the brunettes, [[TeenGenius Sinead Starling]] is the redhead, and [[TheHero Amy Cahill]] falls in between the last two, with reddish-brown hair.
* BluffTheEavesdropper
* BrotherSisterTeam: Amy and Dan; Natalie and Ian.
* CharacterDevelopment:
** Amy overcomes a lot of her shyness.
** Everywhere in Book 10.
** All of the minor characters get this. If you look at reviews of the first book of the series, you'll see critiques of the "one-dimensional" relatives. Stick around until the middle of the series and interesting developments will begin taking place, especially - unusually for a childrens' book series - among adult supporting characters; the younger minor characters' development mostly happens in the last two books.
* ChekhovsClassroom: All the things Grace taught the Cahill siblings came in handy on the clue hunt.
* TheClan: Of the Cahills.
* DeathByOriginStory: Hope and Arthur.
* DependingOnTheWriter: While sometimes there is geniune CharacterDevelopment and the reveal of HiddenDepths, sometimes characters, particularly Ian and Natalie, undergo drastic and rapid personality changes, depending on how an author views them. For example, Gordon Korman tends to portray Ian as hot-headed and his sister as the patient and collected one, while in Patrick Carmen's ''The Black Circle'', Natalie is the one throwing a fit when things don't go as planned while Ian is able to keep his head.
* DisabilitySuperpower: Hinted with [[spoiler: the Starling brothers.]]
* DoesntTrustThoseGuys: "Never trust a Cahill."
* DownerBeginning: The series begins with Grace Cahill's death.
* EveryoneIsRelated: Practically all the main characters are Cahills, with fans who make accounts on the web site also being "inducted" into the Cahill family. (However, it's a very distant relation, with common ancestors only as recent as the early 16th century.)
* EvilMatriarch: Isabel
* TheFamilyThatSlaysTogether: All four branches, due to FeudingFamilies, though the Kabras are the best example.
* FeudingFamilies: The Lucian, Ekaterina, Tomas, and Janus branches are all feuding, especially the Ekaterina and Tomas.
* FoolishSiblingResponsibleSibling: Dan and Amy, respectively. [[CharacterDevelopment Dan gets somewhat better, though.]]
* FollowInMyFootsteps: The reason most of the main clue hunters, including Amy and Dan, want to win the clue hunt, and are so ruthless in the way they go about it.
* FollowTheChaos: Even early on in the clue hunt, Nellie is able to locate Amy and Dan by turning on the news, seeing where's there been some suspicious-sounding trouble, and heading directly to that location.
* GettingCrapPastTheRadar:
** [[Radar/The39Clues It's got its own page]]
* GoofyPrintUnderwear: Dan has Pokemon on his, and Ian has ''pink dollar signs'' of all things on his, even though [[WeAllLiveInAmerica he's from Britian, where the dollar is not used.]]
* GreyAndGrayMorality: Even Amy and Dan, who are by far the nicest and most principled clue hunters, will do morally questionable things from time to time.
* HeelFaceTurn: Oh so many. It might even be a HeelFaceRevolvingDoor for ''every'' Cahill. They all seem to have ulterior motives.
** By ''In Too Deep'' [[spoiler: Irina has basically switched sides and wants to help Amy and Dan -- but of course they don't believe her until the very end...]]
* HufflepuffHouse: Arguably, every single branch. Although [[spoiler: the Lucians managed to get their hands on a vial of something-or-other in Book 1 from Ben Franklin, which then turned out to be the Lucian serum, part of the master serum.]]
* HypocriticalHumor: At one point in the series, Dan complains "I can't believe she cheated me - right when I was in the middle of cheating her!"
* IslandBase: The Ekaterina have one inside TheBermudaTriangle. Also,[[spoiler: Madrigals]] have one on Easter Island.
** There's also [[spoiler: the original island home of the Cahills where the Gauntlet is located.]]
* KillEmAll: [[spoiler: Isabel's plan on Easter Island - she's even willing to kill her own children.]]
* KilledOffForReal: [[spoiler:Irina]] in ''In Too Deep''.
* KissingCousins: Almost any pairing in the book can be considered this seeing as almost every character is a Cahill. This is usually dismissed though, seeing as apparently half of Earth's population is one.
* LeParkour: Created by the Tomas.
* LoadsAndLoadsOfCharacters: Almost every historical figure for 500 years is a part of the Cahill family. That's [[CaptainObvious a lot of people]].
** Also applicable on a smaller scale - there are seven "teams" in the Clue hunt. In these teams, there are, in total, seventeen people. Nearly every one of these seventeen people gets point-of-view chapters in multiple books, as well as a great deal of CharacterDevelopment. Then there are the minor characters, some recurring and some not, and the villains who are not officially part of any team.
* LookBehindYou: When Natalie tells a disbelieving Hamilton that Amy and Dan just entered the building, he's surprised to find out that it's ''not'' a trick to get him to leave her brother alone, and that Amy and Dan really just came in.
* MachiavelliWasWrong: Well, he was certainly right in regards to Ian and Natalie's relationship with their mother. [[spoiler: Until the last book, when they realize that, while they loved Isabel, they were only following her (mostly) out of fear.]]
* MeleeATrois: Between all 7 teams.
* MistreatmentInducedBetrayal: [[spoiler: Irina betrayed Isabel because of the latter's cruel treatment of her (although her "reward" for this was death), and later, Ian and Natalie left their mother after learning that she drank the Lucian serum and did numerous evil things detailed in her secret files. Then, when Isabel tried to kill them, that only sealed the deal.]]
* NarrativeProfanityFilter
* [[spoiler: NoRomanticResolution: Amy and Ian never discuss their feelings or what happened between them in Korea, and [[OneShotCharacter Kurt]] never shows up again after seemingly being set up as Amy's new love interest in the seventh book]].
* OneDegreeOfSeparation: Basically everyone is connected somehow--and practically everyone, Cahill or non-Cahill, knew Grace Cahill.
* OppositesAttract: [[ShrinkingViolet Amy]] [[BrainyBrunette Cahill]] and [[EvilBrit Ian Kabra]]; see UnrequitedLoveSwitcheroo below.
* ParentalAbandonment:
** Amy and Dan's parents were killed in a house fire.
** At the end of the series, Ian and Natalie Kabra apply also, though it's not so much ParentalAbandonment as it is [[spoiler: abandoning their parents.]]
* ParentalIssues: Most of the characters have them.
* PhotographicMemory: Dan has one.
* PlotDrivingSecret: The purpose of the 39 Clues, who the Madrigals are, etc.
* PrivilegedRival: The Kabras, full stop.
* PutOnABus: The Starlings are caught in an explosion rigged by the Holts and end up in the hospital for the next nine books, [[spoiler: but they return in book ten.]]
* ReconcileTheBitterFoes: [[spoiler:This is the goal of the Madrigals, and Amy and Dan manage to bring about a truce between the clue-hunting teams.]]
* [[spoiler:RedemptionEqualsDeath: For Irina]].
* SacrificialLion: [[spoiler: Irina and Lester]].
** Though [[spoiler: Lester]] may be more of a SacrificialLamb, given the fact that he was only around for one book.
* ScrewTheMoneyIHaveRules: Actually a subversion. Amy and Dan aren't above stealing and lying if it means getting any information at all on their parents and the fire that killed them.
* ScrewTheRulesIHaveMoney: Basically every Cahill BUT Amy and Dan
* ScrewTheRulesImDoingWhatsRight: Amy and Dan. (It gets even more so in the SequelSeries.)
* SecretLegacy
* SeriousBusiness: The 39 Clues.
** Although seeing as the prize for finding all 39 is [[spoiler: super strength, intelligence, creativity and strategy skills]] that could grant you world domination... well, the way all the characters take it seriously doesn't seem too farfetched.
* ShoutOut: A lot. To ''Franchise/StarWars, Franchise/StarTrek, Franchise/IndianaJones, Creator/MontyPython, Film/MaryPoppins''...
* ShownTheirWork: [[JustifiedTrope Justified]]. In order to find the clues, Amy and Dan need to research the people and places connected to the clue hunt. Also, it's part of [[TheSmartGuy Amy's characterization to spout historical facts with little prompting.]]
* SiblingTeam: Amy and Dan, Ian and Natalie, the Starling triplets.
* SixthRanger: [[spoiler: The Madrigals are a Cahill family branch]].
* SmartPeoplePlayChess: In the second book, Ian is said to have a very high IQ. In the same exact scene, he plays chess against a supercomputer.
* SomedayThisWillComeInHandy: See ChekhovsClassroom.
* TallDarkAndHandsome: Ian
* TeamPet: Saladin, Grace's cat, who accompanies Amy and Dan on their adventures.
** The Holts have their dog, Arnold.
* TeenGenius: The Starlings.
* TeethClenchedTeamwork: Occurs whenever alliances are formed between teams. Of special note are the Cahills and the Kabras in book 3, and the Kabras and Irina in books 5 and 6.
* ThemeNaming: The Holts are all named after iconic United States political figures. Eisenhower and this twin daughters, Reagan and Madison, are all named after the surnames of U.S. Presidents: UsefulNotes/DwightDEisenhower, UsefulNotes/RonaldReagan, and UsefulNotes/JamesMadison. Eisenhower's wife is named Mary-Todd (UsefulNotes/AbrahamLincoln's First Lady), their son is named Hamilton (presumably for UsefulNotes/AlexanderHamilton) and their dog is named Arnold (Benedict, possibly?).
* ThereAreNoTherapists: Whoo, boy... It'd be easier to name the characters in this series who ''don't'' have some form of mommy/daddy issues.
* TomatoInTheMirror: This should be two living Tomatoes and three dead Tomatoes in the Mirror. ''The Viper's Nest'' has Dan Cahill revealing Cahill's family's branch. It happens to be [[spoiler: Madrigals, a branch known for its secretiveness. The reason is explained at the end of ''Storm Warning'', the Madrigals' main goal is to unite the all five branches of the Cahill Family.]]
* TwinTelepathy: Amy and Dan aren't twins, but they are siblings who are pretty close and always know what the other is thinking by reading each other's facial expressions. Some fanfiction makes it practically telepathy, in any case.
* TwoAliasesOneCharacter: As the series often involves espionage, it's inevitable that this trope comes into play.
* UndisclosedFunds: Readers are never told exactly how rich Grace Cahill is. Even one trading card that lists the wealthiest Cahills and how much they're worth leaves out how much money Grace has.
* UnrequitedLoveSwitcheroo: Amy's always had somewhat of a crush on the fabulous Ian Kabra. After he [[spoiler: "fakes" love for her and leaves her for dead in a cave]] she eventually starts getting over him. Too bad he's [[BecomingTheMask starting to develop genuine feelings...]]
* VideoWills: How Grace starts the hunt for The 39 Clues.
* WeAllLiveInAmerica: See the GoofyPrintUnderwear entry above.
* WellDoneSonGuy: Isabel Kabra for her children and Bae Oh for Alistair, arguably.
** Cora for Jonah
* WhamEpisode:
** ''In Too Deep'': [[spoiler:[[SacrificialLion Irina]] [[CerebusSyndrome dies]].]]
** ''The Viper's Nest'': [[spoiler:[[TomatoInTheMirror Amy and Dan are Madrigals, just like their parents and Grace before them]].]]
** ''Storm Warning'': [[spoiler:Nellie is actually working for Grace and the Madrigals. Then the ending reveals that [[GoodAllAlong the Madrigals are actually trying to bring the Cahills back together]], and that the Man in Black/Gray is Fiske Cahill, [[LukeIAmYourFather Grace's brother]].]]
** ''Into the Gauntlet'': The main plot is resolved with [[spoiler:the Cahills all working together to stop Isabel, then all giving their clues to Dan and Amy]]. But then we get a SequelHook:[[spoiler:there's ''another'' important player, an evil organization called the Vespers]].
* WhamLine: In ''The Viper's Nest'', Grace says that she can't listen to the music of Orlando di Lasso because it's "a sad reminder" of Hope and Arthur's branch. When Amy and Dan have some of di Lasso's music, they find out which branch they belong to because of the title and the above fact:
-->''Mon coeur se reccomande a vous by Orlando di Lasso.\\
'''[[spoiler: A Madrigal, in Four Parts]].'''''
* [[YouKilledMyFather You Killed Our Parents]]:
** Amy and Dan, repeatedly, towards [[spoiler: Isabel, Alistair, Cora Wizard, and the Holts.]]
** [[spoiler: Alistair]] towards [[spoiler: Bae Oh]].

[[folder:Series 2: Cahills vs. Vespers]]
!!'''Warning''': By definition, it is impossible to discuss a SequelSeries without spoiling the first series, so expect '''unmarked spoilers for Series 1''' from here on out.
* {{Adorkable}}: Amy's secret nickname for her boyfriend, Evan.
** Also, the scene where Amy and Atticus are fangirling over old books in ''Trust No One''.
* AirVentPassageway: Somewhat altered in ''The Dead of Night'', in which Phoenix Wizard and Reagan Holt try to escape the Vespers' prison by climbing up a dumbwaiter shaft. Justified, since the characters are children.
* AndThisIsFor: Fiske dedicates a Vesper-kicking to Alistair.
* AnyoneCanDie: Much more deaths than the first series, including [[spoiler:Natalie Kabra, Isabel Kabra, William [=McIntyre=], Alastair Oh, Damian Vesper and Evan Tolliver.]]
* BettyAndVeronica: Male version with Evan as the Betty, Ian as the Veronica, and as of ''Dead of Night'', [[spoiler: Jake Rosenbloom]] as the ThirdOptionLoveInterest.
* BlackAndGrayMorality
* CaperRationalization: Silly Interpol. They aren't stealing because they're crazy criminals; they're stealing because a shadowy, evil organization has kidnapped seven of their family members and require that they steal things as part of the ransom.
* CuffsOffRubWrists: Dan does this after escaping from Agent Vanek.
* CutenessProximity: Sinead toward... ''her gun'' in ''Trust No One''.
* DarkerAndEdgier: There's no doubt that Cahills vs. Vespers is darker than the original series...
** A ''huge'' amount of {{Mook}} deaths occur, many with a healthy dose of NightmareFuel.
** Besides death, there's an increase in violence, and the authors don't shy away from describing blood - see OnlyAFleshWound. And in Trust No One, [[spoiler: Alistair is KilledOffForReal]].
** There are more deaths, both major and total, in ''Day of Doom'' alone than in all of the books of the previous series combined.
** Though the language remains (almost always) kid-friendly, it's obvious that more liberties have been taken than in the original series. For example, "ass" appears once in Trust No One, and "pissed off" also appears twice.
** A LoveDodecahedron shows up in "Dead of Night".
** Also, just take a look at Amy and Dan themselves in comparison with the beginning of the first series... or even the end. It's clear that their experiences have not only made them stronger, but also psychologically damaged them. (See also: [[spoiler: Amy going into HeroicSafeMode]] at the end of ''Trust No One''.)
* EvilGloating: Isabel goes on and on when she kidnaps Atticus.
* FaceHeelTurn: It is revealed that one of the Cahills ([[spoiler: Sinead]]) is a double agent for the Vespers.
* FireForgedFriends: The Cahill family, even if "friends" may be still a stretch in some cases.
* GettingCrapPastTheRadar: [[Radar/The39Clues It's got it's own page]]

* HeadbuttingHeroes: See "FireForgedFriends," above.
* HeterosexualLifePartners: Dan and Atticus.
** Hamilton and Jonah.
** Ian and Evan in ''Day of Doom''.
* HeroicSafeMode: [[spoiler: Amy]] goes into one near the end of Trust No One, even referring to this "calmly observing instead of actually experiencing" side as "Safe [[spoiler: Amy]]" (while the side that is actually living in the situation and experiencing it is referred to as "Scared [[spoiler: Amy]]"). Last we see of [[spoiler: her]] in the book, [[spoiler: she literally takes off running away from the others after learning exactly what the Vespers plan to do (create a doomsday device) and realizing that she has given them the final piece they need to do it and how it has fallen on her shoulders now to stop it]].
* HostageSituation: The premise of the series is that seven Cahills have been kidnapped, and Amy and Dan Cahill have to fulfill bizarre ransom requests to get them back.
* HostageVideo: How the Vespers prove that they have the hostages alive.
* HypocriticalHumor: At one point in ''The Medusa Plot'', [[GeniusBruiser Hamilton]] [[TheBigGuy Holt]] complains that "Those guys ripped off what we rightfully stole!"
* IWillPunishYourFriendForYourFailure: See HostageSituation entry above and RevengeByProxy entry below.
* KilledOffForReal: [[spoiler: Alistair.]]
** [[spoiler: [=McIntyre=]]]
** [[spoiler: Evan, Natalie, and Isabel]]
* LittleUselessGun: [[spoiler: Sinead]] has (and uses) one in Trust No One. (Contrary to what the trope title may make some assume, it's definitely not useless.)
* LongDistanceRelationship: Amy and Evan start one of these (carried on mostly via phone) after Amy and Dan take off on their missions around the world.
* MixedMetaphor: Amy combines "late to the party" with "missing the boat completely" in ''Trust No One'', in what Ian [[LampshadeHanging refers to]] as "that appalling mixed metaphor."
* NoodleIncident: In the bonus track on the ''Shatterproof'' audiobook, Atticus briefly mentions a few incidents from the past, involving things like sonar machines and Stonehenge, without fully explaining them.
* OnlyAFleshWound: [[spoiler: Nellie]] is shot in the shoulder and lives, although she needed to have the bullet removed to do so. Her survival might not be as implausible had the removal been done properly by trained professionals. Instead, the incisions are made by a twelve-year-old and the removal is done by [[SpoiledBrat a thirteen-year-old]], both of whom are inexperienced, and the latter of whom is so [[AfraidofBlood squeamish about blood]] that she has [[FridgeHorror her eyes closed while she removes the bullet]]. In an unsterilized environment, natch.
* ParentalAbandonment: As stated above, [[spoiler: Ian and Natalie. Isabel disowned them.]] Also, Cora Wizard is no longer speaking to her son Jonah, and [[spoiler: Amy and Dan's father is alive, meaning he left them to basically raise themselves for about nine years.]]
** [[spoiler: It is later revealed that the last case isn't true after all, and that Isabel was merely trying to trick Amy and Dan.]]
* RevengeByProxy: When the Vespers think that Amy and Dan are trying to trick them, they shoot [[spoiler: Nellie, but she survives.]]
* RoaringRampageOfRevenge: [[spoiler:Isabel]] goes on one in ''Day of Doom'' after [[spoiler:her daughter, Natalie]] dies.
* SacrificialLion: [[spoiler: William [=McIntyre=]]].
** [[spoiler: In ''Trust No One'', Alistair Oh]].
* ScrewTheRulesImDoingWhatsRight: Amy and Dan climb even higher on the JustifiedCriminal ladder with [[spoiler: the things the Vespers make them do in hopes of getting the hostages back alive]].
* ShownTheirWork: Like in the first series, it's [[JustifiedTrope Justified]]. This time, Amy's joined by Atticus in her love of talking about history.
* TakeMeInstead: Amy tries to trade herself for the hostages.
* TeethClenchedTeamwork: Ian and Evan working together in the Cahill Command Center, though any of the Cahills working together qualify, since they had such a fiercy rivarly before the conclusion of the Hunt.
* ThereAreNoTherapists: Or at least, if there are, [[spoiler: Dan]] hasn't seen any, even if he needs to. (For that matter, several characters need to.)
* TheseHandsHaveKilled: In ''Shatterproof'', this is the instant reaction of [[spoiler: Jonah]] after shooting [[spoiler: Luna Amato]] at point-blank range.
* TimeSkip: Two years have passed since the first series (making Amy sixteen years old and Dan thirteen).
* WeHaveToGetTheBulletOut: See "OnlyAFleshWound" entry above.
* WhamEpisode: Happens constantly:
** ''A King's Ransom'': [[spoiler: William [=McIntyre=] dies, starting the AnyoneCanDie atmosphere. The Guardians are revealed, and Atticus is one. Then Atticus is kidnapped, and Dan gets a text from [[BackFromTheDead AJT]].]]
** ''Shatterproof'': [[spoiler: Erasmus follows Amato to the Vesper base, but she manages to kill him. Then Jonah and Hamilton show up, and Jonah shoots Amato.]] Furthermore, another big reveal happens in the online game, or the beginning of ''Trust No One'' for those who don't play it: [[TheMole Vesper Three]] is [[spoiler:Sinead Starling]].
** ''Trust No One'': After the aformentioned reveal, [[spoiler:Isabel]] comes back. Then V1 says they're done with giving him stuff, after one more: [[spoiler:the Cahill Ring.]] Then we find out what the Vespers are using all of this stuff for: [[spoiler:They're building a DoomsdayDevice.]] Finally, in order to combat them, [[spoiler:Dan drinks the Serum.]]
* WhatHappenedToTheMouse: The trading cards give major hints that [[spoiler: Broderick Wizard, Jonah's father, is a Vesper. Because he appears in the original series and his character is even given a little more depth in the eighth book, it is expected that he will make an appearance in this series, one way or another. He never does.]]

[[folder:Series 3: Unstoppable]]

* BreakHisHeartToSaveHim: When, despite her repeated requests, Jake refuses to stop following Amy into dangerous situations, she attempts to get him to stop by telling him she doesn't have feelings for him, since LetsJustBeFriends didn't dissuade him, either.
* [[HeroWithBadPublicity Heroes With Bad Publicity]]: Amy and Dan become this when a [[{{Paparazzi}} villainous media mogul]] targets them.
* KilledOffForReal: [[spoiler: Pony]]
* LetsJustBeFriends: Amy tells this to Jake near the end of ''Nowhere to Run''.
* MaliciousSlander: Amy and Dan are the victims of this.
* ShoutOut: Jonah calls Pony [[Literature/TheOutsiders "Pony Boy]]" and asks him if he's [[Literature/TheOutsiders "staying gold."]]
* ShownTheirWork: The Cahills and Rosenblooms learn a lot about ancient civilizations as they travel around the world looking for the ingredients of the serum's antidote, and they talk about what they learn a ''lot.'' {{Justified}} in that the information is often crucial to finding the ingredients, and a couple of the characters are [[TheSmartGuy really into history.]]
* WhamEpisode: ''Countdown'': [[spoiler:Amy drinks the original serum, meaning she's going to die. Pierce gets Olivia's book, and starts trying to make a serum without side-effects. Nellie and Sammy are captured by Pierce's company. Finally, Pierce uses the book to set a trap for the Cahills and kidnaps Dan, [[KilledOffForReal and Pony is killed trying to save him.]]]]

[[folder:Series 4: Doublecross]]

* SeparatedByACommonLanguage: Ian has difficulty adjusting to life in America, where he finds that many people misunderstand the British terms he uses.
* ShownTheirWork: The historical facts start popping up on page three, when Ian compares his accomplishments to those of Napoleon.


[[folder:Companion Books]]
The Companion Books include: ''Agent Handbook'', ''Rapid Fire'', ''The Cahill Files'', and ''The Black Book of Buried Secrets''
!!'''Warning''': Unmarked spoilers for Series 1 and possibly Series 2 below.
* BreadEggsMilkSquick: Cora's skills are listed as "painting, sculpture, manipulation, drawing, spying, blackmail."
** Katherine Cahill's are "reasoning, inventing, calculating, analyzing, double-crossing."
** Natalie's interests include "shopping, yachting, manicures, target practice" - target practice for her dart gun, that is.
** Hope Cahill's interests are "archaeology, baking, singing, explosives."
* HolidayAppropriateWeather: In Legacy when it is revealed on Christmas that Grace is [[spoiler: going to die]] it begins to snow.
* ICantBelieveAGuyLikeYouWouldNoticeMe: [[PlayingWithTropes Played with]] in ''Crushed''. Amy finds it amazing that [[TheBeautifulElite a guy like Ian]] is visiting a girl like her. [[TheProudElite Ian finds it difficult to believe, too.]]
* NoodleIncident: ''The Submarine Job'' never really explains the story behind Grace's decision to drive that car off a cliff.
* StalkingIsLove: In ''Operation Trinity,'' set before the clue hunt, Ian watches Amy on one of the Cahill activity surveillance camera feeds his parents keep before heading to dinner, and it's revealed he knows that it's time for the schools in her city let out. The entire, plot-irrelevant scene seems to have been thrown in solely to please the [[FanPreferredCouple Amy/Ian shippers]].
* WellDoneSonGuy: Rupert of ''Silent Night'' really wants his aloof father to notice him.
* YoungFutureFamousPeople: ''The Houdini Escape'' features a young Creator/HarryHoudini, and there is short story about young UsefulNotes/WinstonChurchill in ''The Black Book of Buried Secrets''.
* [[IHaveMyWays Your Mother Has Her Ways]]: In ''Operation Trinity'', Irina tells Ian and Natalie Kabra ''Your mother has her methods" when asked how they obtained information belonging to the Ekats.

* BreadEggsMilkSquick: According to [[http://the39clues.scholastic.com/cahillweb/article/cliqueme-alana-flores her offical social networking profile]], Alana Flores has quite a variety of interests, including "chess, International finance... medieval torture devices, Scottish terriers."
** Chrissy's interests are listed as "cheerleading, dance team, cryptography, kittens, lock picking, gymnastics, karaoke, late-night expeditions." Natalie's are "afternoon tea, Catherine the Great, high fashion, female pirates, target practice, the south of France, fox hunting, being fashionably late."
* DirtyCop: The Lucians have bribed ''many'' a police officer.
* TheFashionista: Lily Chernova loves fashion even more than math.
* RevengeOfTheSequel: [[ParodiedTrope Parodied]] in an online message from the branch heads. Dan apparantly decided to use his new credit card to order ''The Ninja’s Revenge Part VII: The Last Revenge'' and ''The Ninja’s Revenge Part VIII: The Final Last Revenge'' on Pay-per-view.