This is a form of Chekhov's Gun because introducing a secret diary into the show means the audience expects that there will be a plot dedicated to another character finding it and deciding and/or proceeding to read it and/or pass it around their friends, etc. Naturally, the character who owns the diary is furious when they discover this invasion of their privacy.
The Annoying Younger Sibling will typically make it their life goal to find and steal the diary and reveal all of the juicy, embarrassing secrets within to everyone the character knows, for the express purpose of humiliation.
For whatever reason, a lot of these "secret" diaries tend to be left open on the owner's desk instead of tucked away and locked somewhere, ripe and ready for snooping eyes. These circumstances usually play out in Video Games, where the protagonist can easily access a character's private thoughts in a justified fashion in order to drive the plot or just exist as a juicy Easter Egg.
See also Diary.
- A commercial for AT&T U-Verse has the family seated around the dinner table. The son is reading the daughter's diary, which the parents have also read. The daughter is quite pleased. (The theme of the commercial is that having U-Verse makes everybody happy.)
- Played for Laughs in Axis Powers Hetalia when the Allied Forces (America, England, France, Russia and China) obtain Germany's diary, and read it hoping to gain knowledge of how to defeat the Axis Powers (North Italy, Germany and Japan). Instead they find that all of the entries are about Germany's bewilderment with North Italy's behavior.
- Slightly different set-up in Patlabor: Lt. Clancy is preparing a report on the rest of the team before leaving the force, and the others sneak into her apartment to read it.
- Touch: In an early chapter, Tatsuya found Minami's diary. Later Minami accused him of reading her diary. Tatsuya swore that he did not, and it is left ambiguous whether he did or did not. The next day Minami confessed to Tatsuya what it was true what was written on her diary and she is in love with him... Tatsuya got so flustered that she realized that he had NOT read it, so she backpedaled and claimed that she had only written bad things about him.
- Tsukihime: Shiki Tohno finds Makihisa Tohno's hidden diary, in which it is revealed that the Tohno blood line contains demonic blood, that Akiha is one of those who has demonic traits, that Makihisa himself had a split personality, that Kohaku and Hisui are adopted synchronizers who can calm the demon blood by exchanging bodily fluids and that there was indeed a third child with the same name as Shiki that was adopted after Makihisa wiped his clan out.
- Wandering Son has a shared secret diary between the eleven-year-old main characters Shuuichi and Yoshino, in which they write to another about their various trans experiences. When a boy gets ahold of the diary and passes it around, both kids in general and Shuuichi in particular are ostracized. They start a new one not too long after.
- In the ending to the anime version of Tona-Gura!, a pivotal diary that Hatsune gives Kazuki is Kazuki's own forgotten childhood diary which reveals that Yuuji's always been playful; teen hormones now make that playfulness obnoxious and immature, rather than cute. She also sees in it that she herself used to be a great deal more playful, but that she has also not outgrown her childish tendency to want complete control over how things are, especially with Yuuji. This marks a huge turning point.
- In the second season of Yuki Yuna is a Hero, Yuna keeps a "Hero's Journal" where she writes about how she's Secretly Dying because she can't talk about it without spreading the curse to others. Togo and her friends find it when Togo sneaks into her room.
- One Archie Comics story had Betty losing one of her diaries (to be more exact, the one she wrote about her moments with Archie in) and was worried that Veronica would get her hands on it. To make matters worse, Veronica overheard her and offered $100 to anyone who turned it in to her. Fortunately for Betty, Mr. Svenson returned it to her before anyone else could find it.
- In an issue of Generation X, the school is robbed, and Husk's diary is one of the items stolen. Since she often wrote about their adventures, everyone's secret identities were at risk. The thieves were eventually found and convinced to return the stolen items, and thankfully Husk's diary was written off as a bored schoolgirl's overactive imagination. The thieves did enjoy the Purple Prose dedicated to Chamber, however, and one proceeded to read it, embarrassing poor Paige as the Gen X kids died laughing (thankfully Chamber wasn't with them).
- In Cerebus the Aardvark, at the end of the Jaka's Story arc, the Cirinists who are trying to get Jaka to sign an admission of immoral behavior attack her resolve by reading her excerpts from her employer's diary. The little bit revealed shows that he was thinking some very naughty thoughts about her, in stark contrast to his meek and unassuming behavior while they were together, which deeply hurts her.
- A male example: in The Golden Age, Tex Thompson has one, which reveals the truth behind himself and Dynaman, which Joan Dale takes to her friends Lance Gallant and Paula Brooks to open up and discover.
- In America vs. the Justice Society, a diary that supposedly came from the Earth-2 Batman accused the Justice Society of being collaborators with the Nazis and that they spent much of their post-World War II careers covering it up. As it turned out, the diary itself was a hoax created by Batman in order to have them apprehend Per Degaton during a time when he wasn't alive, which would be when Professor Malachi Zee of the Brain Trust would arrive at the present time of the story to finger his murderer.
- In Robin almost all of Stephanie Brown's narration boxes are excerpts the secret journal she keeps relating to crime fighting. Amusingly the secret journal that is found and becomes a plot point comes out of nowhere and belongs to Tim (who was never at any point seen or mentioned as keeping one) and reveals Bruce's secret id to his dad. This incredibly dangerous and ill considered journal containing highly classified information disappears from continuity just as abruptly as it entered and was never mentioned again.
- Wonder Woman (1987): When Diana, Donna and Cassie go to the Kapatelis's home to speak with Vanessa's mother and try to figure out how the teenager was taken and brainwashed despite her former loyalty to Diana and display of resistance to attempts to mess with her mind by Doctor Psycho Cassie finds a Diary hidden in her room. Flipping to the last pages gives them the hints they need to track down those who abducted her.
- One wonders why Paige Fox of FoxTrot even bothers trying to keep a diary when Peter and Jason constantly read it openly. Jason has go so far as to post excerpts from her diary online and has even written in it (apparently on multiple occasions) a confession to really being an ugly alien being.
- Funky Winkerbean: Lisa kept one of these when she was a teen-ager, as revealed during the storyline involving ex-boyfriend Frankie Pierce and his efforts to produce a reality show about a reunion with their biological son, Darrin Fairgood (with the real aim souring the memory of Lisa).
- Evangelion 303: Jessika wrote down in her diary all her private fantasies about Asuka. Her girlfriend read it, mistakenly thought that Jessika had been unfaithful and mailed the pages to Asuka in chapter 11. Shinji, knowing that Jessika would not want to share that with anybody, burnt them.
Shinji: In one breath I was exposed to someones darkest, most hidden, strangest appetites.
- A male example: Boris Sparkle in Rise Of Empress Midnight has a secret diary in the back on one of his research paper, where Twilight finds out that he invented the Alicorn Amulet, she had a sister, and he was the reason her grandfather is dead.
- The recommended Ranma ½ fanfic Genma's Journal has Nabiki finding Genma's secret diary and discovering that Ranma's father is actually a Magnificent Bastard and hiding behind Obfuscating Stupidity rather than the doofus he appears to be.
- A Peccatis starts with Neville and Harry receiving, and having to figure out the meaning of, isolated pages from Dumbledore's diary.
- In Shrek 2, Shrek goes through Fiona's childhood diary, in which she explained her dreams of meeting her Prince Charming and living happily ever after, which only serves to fuel his guilt about Fiona changing for him.
King Harold: S-Sorry. Uh...I hope I'm not interrupting anything.
Shrek: No, no, no. I was just reading a... a scary book.
- In When Marnie Was There, Sayaka finds Marnie's diary and shows it to Anna upon which the latter realizes that she just imagined her encounters with Marnie.
- In 3 Women, Millie has a diary protected with lock and key. Nonetheless, her roommate Pinky later manages to get a good look inside.
- The Princess Diaries had a scene which Mia Thermopolis received her personal diary (as a young princess) after she got the locket from her paternal grandmother earlier (hence the name of the Disney Princess movie), renaming it as "Mia's Diary".
- In Parasite (2019), Ki-Woo's first act of debauchery in the Parks' house while they're away is to steal Da-Hye's secret diary and read it. He later has to scramble to return it once the Parks come home early.
- William Sleator's Others See Us uses two stolen diaries as the MacGuffin, with the inversion that the thief didn't steal them to read them, because she's telepathic and knows the contents already.
- Harry Potter
- In Harry Potter and the Chamber of Secrets, Draco Malfoy plans to do this when he finds Tom Riddle's diary among Harry's possessions and mistakenly thinks it's Harry's diary.
- According to Word of God, the way Riddle's diary uses Ginny is a serious Deconstruction of this trope, foregoing others reading the diary and instead making the diary itself a malevolent entity. J. K. Rowling finds diaries to be "really, really frightening" due to her sister confiding her innermost thoughts to a diary only to worry about people reading.
- Subverted in the Liavek story "Paint the Meadows With Delight" by Pamela Dean, where the main character steals her sister's diary in hopes of figuring out why she's been acting so strangely, and, since she can't read the language it's in, tries to get an older relative to translate it for her. It says much about the family involved that Jehane didn't realize what she had done was objectionable until she got called out on it.
- Happens in Charlotte MacLeod's novel The Family Vault. Caroline Kelling, blind and deaf, embroiders her diary on drapes with the equivalent of Braille.
- Also happens in Charlotte MacLeod's novel Vane Pursuit, in which Elisa Alicia Quatrefages keeps one.
- Zan's entire experience in Norma Fox Mazer's Saturday, the Twelfth of October is set off by her wise-ass brother reading her intimate diary to his friends. At the end Zan is still writing diary notes, but wisely stores them in a bank deposit vault.
- In J.R. Lowell's Daughter of Darkness, Willie Connolly's journal is mentioned very early on. A practitioner of Ritual Magic since the age of eight, she keeps her book with her paraphernalia locked in a desk drawer. Her anthropologist Uncle Jonathan knows about the Black Magic spell she cast on her father's fiancée. Sure enough, he discovers the drawer, breaks into it and reads the journal, taking it with all the evidence to show her father. Unfortunately for him, Willie is invisibly sitting nearby.
- Lawrence Block's Ariel has a rare Secret Diary that remains safe all the way through the story:
I couldn't see myself buying one of those books that say things like My Secret Thoughts in gold on the fake leather cover. They have locks a baby could open with a toothpick, if a baby happened to have a toothpick, and all Roberta [her adoptive mother] has to do is find a locked book called My Secret Thoughts. It would be like writing Be Calm and Relaxed on a red flag and showing it to a bull... So instead of a diary I have this notebook, and instead of hiding it where I'd never find it but Roberta would, I'll keep it in my schoolbag with all my other notebooks. Yes, like The Purloined Letter... Roberta could never resist a diary, but who on earth would want to read a kid's dumb notebook?
- In Wintersmith, the Nac Mac Feegle have a great problem with the idea of a secret diary. Why would Tiffany write her thoughts down in a book with a lock on it which she keeps hidden at the back of a drawer if she didn't want anyone to read it?
- In the mystery novel The Short Drop, a man finds a copy of The Lord of the Rings that belonged to his close family friend, who has been missing ten years. The margins are completely full of multicolored notes. These turn out to be years' worth of coded messages to the people around her, using their favorite colors to clue them in. The main character and the missing woman's mother eventually decrypt the truth: she disappeared because she was pregnant with her father's baby.
- Spoofed in one of the Kangaroo stories by Marc-Uwe Kling where the Kangaroo writes a diary to no other purpose then to "confess" doing something the narrator already suspects him of in order to invoke a violation of privacy when he is unavoidably found out.
- Hetty in Hetty Freather secretly reads Janet's diary and discovers her crush on Jem.
- Buffy the Vampire Slayer shows that Buffy keeps a diary, or at least did in a Season 1 episode. And she promptly freaks out when she thinks Angel might have read it (he didn't).
- The Dukes of Hazzard:
- "Dear Diary" From Season 4, Rosco uses his diary to document (surprisingly, very well and down to the last detail) Boss Hogg's criminal activities, and plans to keep it secret between him and Boss. However, two crooks that Boss had double-crossed years earlier learn about the diary, come to Hazzard and steal it, planning to turn Boss in once and for all, forcing Bo and Luke (who have also learned about the diary) to make a tough decision.
- "Go West, Young Dukes" From the final season, although the only secrets exposed in this diary are those that clear up what really happened during a land transaction 100 years earlier by the ancestors of the Duke and Hogg families. Only Uncle Jesse knew about the diary beforehand, making the trope a literal interpretation.
- In the Disney Channel sitcom Austin & Ally, the title character Ally has a diary that also functions as her songbook. The 3rd episode has Ally lose the diary and Austin finds it. He reads the diary and mistakes Ally writing about the crush she has on the Cell Phone Accessory Cart guy to actually be about himself. Hilarity Ensues. It also results in an Anchored Ship moment for the Austin/Ally pairing.
- Another Disney sitcom Jessie also has this. In one episode, Zuri looks into Jessie's diary on the computer. This leads to a Mistaken for Aliens subtext.
- H2O: Just Add Water: Cleo initially keeps a diary about her newfound mermaid powers. Her sister Kim finds it and tries to expose the girls' secret. Kim mistakenly thinks Miriam is a mermaid too and when she realises her mistake, Cleo pretends the diary was just a school assignment about rewriting fairy tales, and destroys it after.
- In House, House steals his ex-common law wife's psychiatrist's notes (mostly about how her relationship with her husband sucks and she has the hots for House again) and recites them to Wilson a few days later.
- Torchwood has a particularly amusing example in the episode "Adam." Ianto keeps a diary, which is not surprising considering how precise and orderly he is. But that diary apparently also contains, ah, details of his relationship with Jack, which, when Jack finds and reads the diary, leads to the immortal line, "Measuring tapes never lie."
- Red Dwarf: Rimmer walks in and finds Dave "waits for the film to come out" Lister reading. When he asks what the book is, Lister flat-out states that it's Rimmer's diary, then repeats some choice excerpts. Then:
Rimmer: I don't believe it! You've been reading it out to the Cat?!
Cat: Only the best bits!
Lister: So you've read my diary.Rimmer: Yes, but at least I have the common decency to do it sneakily behind your back.
- Mild subversion here is that Rimmer isn't really surprised Lister's reading his diary: he's upset he's doing it publicly.
- Titus: Teenage Christopher comes home to find his father reading his diary to his poker buddies.
- One scene in Spaced shows Tim reading Daisy's diary: "Ha, ha, ha, thrush!"
- Done in The Partridge Family with Keith finding Laurie's diary. Embarrassing for her, since she tended to embellish the truth... quite a bit. She ends up finding a love letter from his girlfriend, and they arrange a swap.
- The 2point4 Children episode "We'd Like to Know a Little More About You For Our Files" has Bill reading her son David's diary, and becoming convinced he's in a relationship with an older woman.
- Played for Laughs in Derry Girls. The first episode begins with a very serious narration about life growing up in the conflict, only for a cut out to reveal Erin being angry at her annoying younger cousin Orla for stealing and reading her diary. Later in the same episode the diary is confiscated and read by a nun at school, and Erin tries to steal it back as soon as she can.
- In Twin Peaks, Laura Palmer kept a diary that becomes a MacGuffin in Season Two as multiple characters look for it for clues on who killed her. Harold Smith, her reclusive confident, held some pages, leading to a struggle for possession of them that paints suspicion on him which eventually drives him to suicide. A defictionalized version was published as a book, The Secret Diary of Laura Palmer which provides pseud-canonical insights into events of the series.
- Lily keeps a diary in So Awkward. Subverted in that it is never especially important to the plot, but she does once have a nightmare where her mother is teaching a class on the psychology of the teenage girl by reading extracts from the diary to her class.
- Neil Sedaka (writer of "Stupid Cupid") has a song called "The Diary", which is about the singer wanting to look into a girl's diary to see if she writes about him in it. The song was written after he asked Connie Francis, who he wrote songs for, for permission to see her diary for inspiration and she refused.
- Bread has the song "Diary". The singer sneaks a look at his beloved's diary, believing when she writes about her "true love" it's himself. When he discovers it's about someone else, he vows to support their relationship.
- The Adventure Zone: Balance has the diary of Sheriff Isaak, which reveals what happened to Jack and June.
- By following hints in Illusion of Gaia, players can find Kara's diary, which the game insists is secret. It's basically just an Easter Egg - there are no penalties or bonuses for reading it.
- One mission in Bully has you recovering a nerdette's diary before a teacher publicizes it.
- In Paper Mario: The Thousand-Year Door's sixth chapter, a ghostly Toad asks you to get his diary from the baggage area and threatens you against reading it. The game gives you the option to read the diary anyway, and after asking things like "wait, seriously really?" and "OK, let's think this through for a little bit" you actually can read the first page before the ghost appears and kills you.
- In the first game, Peach actually can read the secret diary, and indeed she has to in order to advance the plot. It belongs to Bowser.
- Luigi also has a secret diary in the first game, but it's optional and Luigi never finds out you've been reading it.
- It's never seen, but in the first villain interlude in Super Paper Mario, Dimentio muses that he thought Mimi's ideal world was "a gem-filled pool with hunky lifeguards". In response, she turns into Bowser and asks if he's been reading her diary.
- In the Trauma Team game for the Wii, there's a Forensics chapter. The third case gets incredibly disturbing when the diary of Alma is found, and it depicts her descent into insanity, due to her prefrontal lobe tumor, from a loving mother and wife to a psychotic 'Beast of the Lord' who wants to kill her daughter and paraplegic husband in order to let them all go to Heaven together.
- In Animal Crossing: Wild World for DS, a snooty female character sometimes finds (buried underground) diary owned by someone else (most likely a normal female). She asks you if it is ok to read that. If you say so, you are asked where to start.
- Averted in Beyond the Alley of the Dolls, where you can have a conversation with a former villain and ask to read his personal diary, since it may contain important information.
Max: Can we read it?! We promise to laugh at your bad poetry and schoolboy crushes!
- Not so surprisingly, he refuses. Sam comments that it probably wouldn't be useful anyway, because " like any supervillain, his handwriting is as indecipherable as it is crazy".
- Harvest Moon:
- In the games A Wonderful Life and Another Wonderful Life, you can read your child's diary where they write about their relationship with you, their career aspirations, etc.
- In all the Harvest Moon games "writing" in your diary is how you save the game.
- In Baldur's Gate II Irenicus keeps diaries about his experiences and to counteract his failing memory. They're the source of most of your information about him, as he feels "you warrant no villain's exposition from me".
- Subverted with Katys Diary in BoxxyQuest: The Gathering Storm. Its in a secret location, but the opening lines encourage the finder to read it, because she wants to share her story with fellow adventurers.
- Divinity: Original Sin II: One newlywed NPC keeps a secret lair with a diary that details his plan to marry for money and then murder his father-in-law to speed the inheritance. If the player chooses to save the father-in-law, they can give the diary to the wife to bypass the usual Persuasion test to convince her.
- In 6teen there is an episode where Jonesy finds Jen's diary at the lost and found. Kaitlin starts reading it out loud at the fountain.
- The Chipettes in the episode of Alvin and the Chipmunks "Dear Diary" learn from their Nanny what a diary is, and each start keeping their own. Wanting to know who is asking who to the dance, the girls start secretly reading each other's diaries and tensions rise when they find unflattering comments written about each other. As revenge, each girl tries to one-up the other by asking their date to the dance, but find the wrong person. Realizing they were all at fault for violating each others privacy and jumping to conclusions, they make up and decide to spend the night together.
- Arthur, "Sue Ellen's Lost Diary": Sue Ellen loses her diary at the library. Arthur and the others find it and are tempted to read it, but decide to just give it back to her instead.
- In Bob's Burgers, Linda reveals that she reads Tina's diary. She says she mostly skims it to make sure she's not on drugs. Helpfully, Tina writers "I'm not on drugs" in the book.
- In the CatDog episode "Curiosity Almost Killed the Cat", Dog starts keeping a diary after Cat (who has one of his own) introduces him to the concept, along with the rule that it's wrong to look in someone else's diary. However, Cat finds himself unable to resist taking a peek, and Dog is understandably upset when he finds out (especially since one of his diary entries called Cat the most trustworthy person he knows).
- Code Lyoko:
- "Logbook": It's all made worse by the fact that Ulrich, the diary's writer, mentions XANA and Lyoko. In the same episode, it's revealed that Sissi also has a secret diary.
- Later repeated with Yumi's diary in "Lost at Sea".
- And then again with Jérémie's logs in "Echoes". Really, one has to wonder why they keep writing these things down.
- In an episode of Doug, the main character's journal gets taken and he spends the entire episode trying to get it back, only to find that school bully Roger Klotz had found it. Fortunately for Doug, Roger was unable to read his handwriting and get at his secrets.
- Ed, Edd n Eddy, "For Your Ed Only": Eddy finds Sarah's diary, and Ed and Edd try to return it before Sarah finds out they peeked and beats the living daylights out of them. Luckily for Eddy, Jonny 2x4 (along with Plank) was stuck on a wall (his head was also stuck on Eddy's shoe) by Sarah.
- Done in The Fairly OddParents with Timmy reading Vicky's secrets and Wanda helping Timmy just because in the diary Vicky says that "the pink squirrel looked fat!". And Cosmo is not happy with them doing it.
Cosmo: A diary is where a girl...And me...Can express their feeling without being judged.
- An episode of Family Guy had the family, except Meg, gather in the teen girl's room while Lois regaled them with pages from her diary, to everyone's laughter. Enter Meg, who proclaims she hates them and runs out of her own room crying. In response, Peter cracks open a beer and encourages Lois to continue reading.
- Trina Riffin has one in Grojband and it's where the band gets their song ideas from.
- Hey Arnold!!, "The Little Pink Book": Said book is Helga's diary. Helga removed and ate the page revealing her name, just before Arnold would have gotten to it.
- An episode of Hi Hi Puffy AmiYumi has Harmony trying to steal the girls' diary to find out all their secrets. When she finally reads it, she is distraught because she already knows all the stuff in it.
- In Jem, the Misfits get Kimber Benton's diary and use it against her. They release it to a popular magazine and it causes a scandal. Luckily, she kept her Cool Big Sis' secret.
- A Rocko's Modern Life episode has Heffer and Rocko finding Filburt's personal journal and cannot resist temptation to read it. As they read, they find out that Filburt is part of an alien race that is planning to take over the earth. Filburt later explains that the journal is actually a science-fiction novel he was working on and none of it is real. Or IS IT?
- The SpongeBob SquarePants episode "Little Yellow Book" has Squidward finding SpongeBob's diary and spilling out his secrets to everyone.
- In the Total Drama Island episode "Not Quite Famous", Heather read Gwen's diary aloud on national television to humiliate her. Notably, even Chris considers this a low blow.
- In The Weekenders, Carter peeks at Tish's diary and finds out that she's moving away. It turns out, though, that it wasn't her diary he found—it was her novel, "Diary."
- The infamous diaries of British Conservative politician, compulsive womanizer and professional Magnificent Bastard Alan Clark were a straight example while he was writing them. Once he was safely retired he sold them to a publisher and sat back to enjoy the show as various colleagues in government, journalists and other public figures were allowed to learn what he really thought of them.
- Marie Curie wrote diary notes for about six weeks after her husband Pierre's tragic death. For her biography Madame Curie, Marie's daughter Eve transcribed a few entries. But there's much more in the recent biographies Marie Curie: A Life by Susan Quinn and Obsessive Genius, the Inner World of Marie Curie by Barbara Goldsmith. Most of these notes are written in the form of letters to Pierre, and Marie was not being metaphorical; she intended for him to read them. She and Pierre were intrigued by spiritualism, attending more than one Spooky Séance accompanied by renowned chemist Sir William Crookes, who was also head of the British Society for Psychic Research. When Marie was rejected by the French Academy of Sciencesnote she felt Pierre come to her and tell her not to worry, she would be elected next time.note
- One of the most famous secret diaries of the early 20th century was kept by actress Mary Astor, whom you'll be familiar with from The Maltese Falcon and Meet Me in St. Louis. It fueled a huge court fight and Hollywood scandal (part 2 here - part 3 here) around Astor's post-divorce attempt to get full custody of her daughter (she didn't). She had written about many affairs including lavish descriptions of playwright George S. Kaufman (let's just say Bigger Is Better in Bed and let it go at that) in glorious detail. Her husband had had affairs too but Double Standard & all that. Lurid excerpts were reprinted in the tabloids amid endless speculations. Thank God Edward abdicated the British throne to marry Wally or we might all still be hearing about it. If you're interested, look up The Purple Diaries by Joseph Egan.