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A mysterious note from a stranger changes the plot in some way. Generally, it is shoved under or into something such as a locker, postbox, or a door. If the recipient sees the note drop on his mat and dives for the door, he will occasionally catch the messenger in the act of posting the note; however, the messenger usually leaves so fast it's as if he teleported.

Can be anything at all, for example:
* A clue from an anonymous source
* A note from a past or future self
* A revealing tape of some kind
* A threat of some kind
* Ransom demand
* Invitation
* etc.

Not to be confused with BrownNote or any other sound related trope, although it can contain, or be a recording of any kind.
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!!Examples:

[[foldercontrol]]

[[folder:Anime & Manga]]
* ''Manga/FairyTailBlueMistral'': When Wendy arrives at Nanalu village, she finds out there's no one there named "Ryuu", the name of the person who wrote the request.
* In ''Manga/OresamaTeacher'', both Mafuyu and Hayasaka receive notes in their lockers saying "360 degree warning". This presages the appearance of a new character, a wacky fake 'ninja' who is trying to destroy the Public Morals Club.
[[/folder]]

[[folder:Fan Works]]
* The Fanfic/AllGuardsmenParty's [[AllegedCar discount spaceship]], the ''Occurrence Border'', is covered with little yellow post-it notes bearing helpful messages such as [[GravityScrew "The gravity in this corridor is tilted 37 degrees to the left"]] or, all too often, [[DontTouchItYouIdiot "Do not ever touch this button."]] That's in realspace, though, once the ship lurches its way into [[HyperspaceIsAScaryPlace the Warp]], more notes start showing up in areas the party has already visited, with always helpful but disturbingly specific advice like "In case of bad dreams check [[FantasticRadiationShielding Gellar Field]] [[OhCrap integrity."]]
* In ''Fanfic/HarryPotterAndTheMethodsOfRationality'', one of the results of Harry's experiments with a [[FantasticTimeManagement Time Turner]] is a note from his future self reading only "DO NOT MESS WITH TIME".
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[[folder:Films -- Animated]]
* ''WesternAnimation/TheIncredibles1''. The "note" is in the form of a digital tablet with a video message inviting Mr. Incredible to do secret superhero work.
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[[folder:Films -- Live-Action]]
* ''Film/OneBR'': After a day or two of staying at the apartment, [[TheProtagonist Sarah]] receives a note that's slid under her door. It tells her that she's in violation of the building's "No Pets" policy, which has an additional notice written on it in red capital letters that more-or-less says "[=SOME=] [=TENANTS=] [=ARE=] [=ALLERGIC=] [=YOU=] [=SELFISH=] [=BITCH=]".
* ''Film/{{Memento}}'': The hero receives a few of these. Some of them from himself, since he suffers from anterograde amnesia.
* ''Film/MurderByDeath'': While Sam Diamond and Miss Skeffington are in their room, they hear a ticking sound. A note is slipped under their door that says, "That ticking sound is a bomb that will go off in 30 seconds. Signed, The Murderer."
* In ''Film/SherlockHolmesAndTheSecretWeapon'', Holmes receives an envelope that is supposed to contain a coded message from Dr. Tobel, containing vital information regarding the bomb sight. However, when he opens the envelope, he finds the coded message has been replaced by a taunting note from Professor Moriarty.
* In ''Film/{{Unsane}}'', a horror/thriller author receives one about a series of murders related to his latest book.
[[/folder]]

[[folder:Literature]]
* A couple of these appear in ''[[Literature/AuntDimity Aunt Dimity Takes a Holiday]]''. The notes' author employs the classic pasted-letters-cut-from-printed-material technique.
* ''Literature/TheFamousFive'': In ''Five Fall into Adventure'', after George is kidnapped, the Five receive a threatening typewritten note, demanding a specific notebook belonging to Uncle Quentin, and warning them not to leave the house to warn the police.
* Mysterious poison-pen letters (together with pranks and outright vandalism) are part of a plot against Shrewsbury College, Oxford in ''[[Literature/LordPeterWimsey Gaudy Night]]''.
* ''Literature/DeadEndJobMysteries'': In book 8, Helen starts getting anonymous threatening letters in the mail, which she figures are related to her current murder investigation. It turns out to be her ultra-religious mother trying to stop her upcoming wedding, since she doesn't believe in divorce and therefore considers Helen to be still married to her first husband.
* In ''Literature/TheGirlFromTheMiraclesDistrict'', [[spoiler:Ture]] leaves Nikita a note serving as a SequelHook, promising her that "the truth" is hidden in a remote Norwegian village.
* ''Literature/{{Home}}'': Frank Money receives a note that says, "Come fast. She be dead if you tarry." This causes Frank to start his journey home to save his sister.
* In ''Literature/TheHoundOfTheBaskervilles'', Sir Henry Baskerville receives a message consisting of words cut and pasted from the ''London Times'' warning him to stay away from the moor (where Baskerville Manor was).
* Parodied in ''Literature/LordsAndLadies'', when Verence receives a technically-anonymous note which, in eccentric spelling, advises him to deal with Magrat's indecision over marriage by simply taking the decision out of her hands, gets sidetracked to point out that witches don't pay taxes and this should continue, and is signed "A Friend (Mss)". Whether this has anything to do with the witch who knows what's best for everyone, has eccentric spelling, and signs herself "Esmeralda Weatherwax (Mss)" is for the reader to determine.
* ''Literature/MonsterOfTheMonthClub'':
** The card Rilla received announcing she'd gotten a free membership to the Monster of the Month Club. [[spoiler:She finds out late in book 1 that it was a present from family friend Mr. Tamerow, who thought the monsters were just plush toys.]]
** Later on, Rilla sends her classmate Joshua Banks (whom she has a big crush on) an anonymous Valentine, saying "Let there be love". He's not as oblivious as she thinks though, figures out it's her and sends back a signed note saying "Let there be friends" in the same style.
[[/folder]]

[[folder:Live-Action TV]]
* Mysterious notes or objects are often the catalyst for Scott Wolter's investigations on ''Series/AmericaUnearthed''.
* In the Spanish series ''Series/ElInternadoLasCumbres'' León, the music teacher, receives a blank envelope. Inside there is a photocopy of a newspaper clipping with the headline "Kidnapper of girl in Lisbon remains at large"[[note]]Original Spanish text:Continúa el paradero desconocido del secuestrador de una menor en Lisboa.[[/note]] and an attached note reading "TEN CUIDADO" (BE CAREFUL).
* In an episode of ''Series/MagicCity'', an envelope is shoved under the door. When opened, it contains a photo with "$20,000" written on the back. The photo shows one of the heroes in bed with a mobster's wife and is clearly an attempt at blackmail.
* ''Series/MurderSheWrote'': In the opening chapter of the ExpandedUniverse novel ''Rum and Razors'', Jessica's been getting strange notes, all consisting of a single line - "GLOTCOYB", each time followed by varying punctuation (none on the first, a question mark on the second, a comma on the third, a period on the fourth and three exclamation points on the fifth). Shortly after finishing her latest manuscript, she sees a group of people outside her home, holding a banner with the same word. It turns out to be her friends Dr. Seth Hazlitt and Sheriff Morton Metzger, plus some other locals, who reveal "GLOTCOYB" is actually [[FunWithAcronyms an acronym]] for "Good luck on the completion of your book". Jessica is both irked and relieved, since the pranks had actually been making her rather nervous, to the point where she answered the door that day with a fire poker in hand to ward off any potential threats.
* In ''Series/TheXFiles'', Agent Mulder repeatedly receives revealing documents on various conspiracies from his informants. They try to be sneaky about it.
[[/folder]]

[[folder:Pinball]]
* In ''Pinball/WhoDunnit1995'', HardboiledDetective Nick Spade receives an unsigned note asking him to meet someone in the basement of Tony's Palace. It's actually a setup for an ambush by the murderer.
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[[folder:Video Games]]
* ''VideoGame/ANNOMutationem'': At the Flores household, Ann can examine Ryan's computer to find that he received an anonymous e-mail from an unknown source telling him to visit a certain location to learn details on finding [[{{Panacea}} N540]].
* ''Franchise/{{Danganronpa}}'':
** ''VisualNovel/DanganronpaTriggerHappyHavoc'': At the end of Chapter 3, Makoto discovers a hidden room, and amidst it he finds a cryptic message stating "[[spoiler:You must not leave.]]" that momentarily gives him [[DejaVu a sense of unease]] just before a MalevolentMaskedMan attacks him from behind.
** ''VisualNovel/Danganronpa2GoodbyeDespair'': The MindScrew ending of Chapter 5 involves [[spoiler:Nagito]] leaving a final message that unveils the true nature of the island, except the important details are obscured by BlackSpeech.
** ''VideoGame/DanganronpaUltraDespairGirls'': Komaru finds her name written in blood at a torture chamber. Later on, she's convinced into seeing that [[spoiler:her parents wrote the message before they died]], which makes her nearly cross the DespairEventHorizon.
** ''VisualNovel/DanganronpaV3KillingHarmony'': A good portion of the final chapter is focused on the survivors trying to find out [[spoiler:Rantaro]]'s true identity, which leads them to a mysterious video recorded by himself that eventually give them a clue to uncover the truth regarding his murder as well as the mastermind's identity.
* ''VideoGame/TheDreamMachine'' has it's main plot started by one Viktor finds in his new apartment.
* You can get these from couriers in ''VideoGame/TheElderScrollsVSkyrim''. The most common and benign are letters from "a friend" who heard you [[SuperScream Shouting]] somewhere and give you directions to another Word of power you can use as you develop your Dragonborn skills. More ominous is an anonymous note you receive if you start looking into the [[MurderInc Dark Brotherhood]], which consists of nothing but an image of a black hand and the words "WE KNOW." [[spoiler:The next time you sleep after getting this note, you'll be kidnapped by one of the assassins, who makes a macabre recruitment offer.]]
* ''VideoGame/{{Fahrenheit}}'': Carla receives an e-mail with only the name "Kirsten", when she looks it up in the police database, she discovers it's a [[ClassifiedInformation classified case file]], which she later learns is more connected to her current investigation.
* ''VideoGame/MetalGear2SolidSnake'': Gray Fox sends Snake anonymous support during his mission in Zanzibar.
* ''VideoGame/Persona4'': Yu receives a warning letter from the killer demanding to stop rescuing anymore people. He then later receives another one in the form of a threat, which [[spoiler:contained the clue the team needed to learn Namatame isn't the one who wrote it]].
* ''VideoGame/SilentHill4'': Henry can receive messages from the dark world if he slides blank pieces of paper under his door. [[ShameIfSomethingHappened Better go check on your neighbor!]]
* ''VideoGame/WorldOfWarcraft'': At the start of the Mists of Pandaria legendary questline, you receive this [[http://www.wowhead.com/item=87261/mysterious-note conveniently named item]], indicating that the last of the Black Dragons wishes to recruit you to save the world.
[[/folder]]

[[folder:Web Comics]]
* In ''Webcomic/AutumnBay'', IntrepidReporter Felicia Kingsley receives one from "a friend" when she is supposed to meet a contact. It is pinned to a post and has her name on it.
[[/folder]]

[[folder:Western Animation]]
* ''WesternAnimation/{{Hilda}}'': In the first episode, the little people leave one in the form of an eviction notice on Hilda's front doorstep.
[[/folder]]
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