Alice and Bob are having a Secret Relationship of some sort, and as part of it, they exchange letters. The nature of these letters is romantic, erotic, or both. They are labeled as from one party and to the other, containing both Alice and Bob's names. In old times, the letters were handwritten, though nowadays, emails and texts are more likely.
Thanks to the Rule of Drama, having written evidence of their affair is going to get messy. This can go down a few different ways.
- Blackmail: Charlie knows—or at least suspects—that the letters exist, and actively seeks them out to use as blackmail against Alice and Bob.
- Revenge: Alice and Bob are exes, and Alice threatens to use their letters as blackmail against Bob. In this situation, Alice usually has less to lose from their exposure than Bob—perhaps Bob was cheating on someone while she was single. Alternative, it may be a Taking You with Me scenario, where Alice is willing to take the backlash from the letters if it means hurting Bob. Alice may be a Woman Scorned.
- Accidental: Charlie stumbles across the letters by accident. Usually Charlie is not the person Alice and Bob really don't want to know—Charlie tends to be a third, unrelated party of some sort. Now Charlie is the Secret Keeper, or the Secret Secret-Keeper. Charlie has to decide whether or not to tell someone. If Alice and Bob know Charlie knows, they will beg, bribe, and threaten Charlie not to tell. Charlie will likely find that Keeping Secrets Sucks.
- Paternity: The letters in these examples can be found in any of the above-mentioned ways, but are connected by their theme. These are letters, documenting a usually-long-ago affair that either makes the paternity of a baby conceived around that time questionable, or outright proves that it's not the child of the presumed father.
- The Vision of Escaflowne: A Paternity example, where Princess Millerna finds letters between her late older sister Marlene and Allen Schezar confirming that her son Prince Chid is actually Allen's and was conceived before she married the Duke of Freid. For worse, Millerna herself has feelings for Allen, making all of this even more awkward.
- The Familiar of Zero: Narrowly averted Blackmail version. While young, Prince Wales of Albion and Princess Henrietta of Tristain fell in love and she at one point sent him a letter declaring her eternal love. Reconquista wanted to get hold of the letter as its contents would prevent Henrietta's marriage to the Germanian Empire and the military alliance of the two nations. Henrietta predicted this and sent Lousie and Saito to retrieve it first.
- A Paternity example: In the Avatar: The Last Airbender The Search comic, Zuko finds letters from his mother Ursa to her former lover Ikem to that seem to indicate his father wasn't actually Fire Lord Ozai. His father actually is Ozai, but Ursa wrote this specifically to see if her letters were being intercepted—which they were—and even though Ozai knew it was a lie, he decided to treat Zuko like he wasn't his son anyway just to spite Ursa. Zuko destroyed the letter afterwards
- Accidental example: In About Schmidt, retired life actuary Warren Schmidt finds letters written by his co-worker Ray Nichols. Those letters implicate Ray having had an affair with Warren's late wife Helen. Warren furiously goes on a rampage to "correct" this situation by destroying all of Helen's belongings, throwing the letters back at Ray and finally giving him a No-Holds-Barred Beatdown.
- In The Great Houdinis, Harry has an affair with Daisy White. A medium obtains some of the letters exchanged and tries to use them against Harry during the congressional hearing.
- Paternity example: In The Black Adder, a Scots lord informs Edmund of love letters between the lord's father and Edmund's mother the queen, detailing an illicit love affair. Edmund tries to use them to prove his elder brother illegitimate, but it turns out that Edmund is the love child instead. He promptly declares them libelous fakes and burns them.
- In season 1 of Downton Abbey there's a Revenge version: Thomas and the Duke of Crowborough were lovers once, and Thomas—who's a big fan of blackmail—threatens the Duke, saying he'll show their letters. The Duke burns them before Thomas gets a chance, though.
Duke: You know, my mother's always telling me, never put anything in writing. And now, thanks to you, I never will again.
- The George Lopez Show: In one episode, George and Angie find old, unopened letters that clue them in that both of them were cheating. Subverted; it turns out that Benny wrote both letters and planted them to screw with their heads.
- In an episode of M*A*S*H, Major Houlihan is very upset after receiving a passionate letter from her husband, Donald Penobscott, that's addressed to a woman named Darline. To add insult to injury, the letter mentions her as "a hard worker" and "sturdy". In the end, she decides to get back at him by sending him back an equally passionate letter addressed to a guy named Hank. The two divorce in a later episode.
- And Then There Were None: General MacArthur figured out his wife Leslie was having an affair with his Number Two Arthur when he received the letter she'd sent her lover. He pulled a successful Uriah Gambit on Arthur during WWI, but the guilt caused him to retire early (and Leslie never recovered from her lover's death). This is why Judge Wargrave summoned him and other murderers to the island, since he wanted to kill them all as punishment for deaths that they got away with: he kills the General soon and rather swiftly, via hitting him on the head with a large rock.
- Chronicles of the Kencyrath
- An Accidental version: The famous courtesan Melissand is having an affair with the "virgin" wife of the richest man in the city. They exchanged letters, and they panic when Jame inadvertently steals those letters (which were hidden inside the object she meant to steal).
- A Blackmail version: In a backstory scene, we see how when she was young, Rawneth got let into Kinzi's room where she dug through her possessions until finding an old love-letter from Kinzi's lover Adiraina. Rawneth tries to blackmail Kinzi with it, though Kinzi shut her down.
- In Like Water for Chocolate it looks like Gertrudis has a Chocolate Baby from cheating on her Colonel Badass lover Juan, until her sister Tita finds letters that showed their mother Elena had an affair with a mulatto man (a slur for half black and half white people), and that Getrudis was the result of such an affair. She shows Juan the letters and clears up Gertrudis' name.
- A paternity example in The Nikolai Duology. The queen of Ravka wrote a bunch of love letters to Magnus Opjer with whom she was having an affair despite being married to king Alexander. This later causes some problems for her already rumored to be illegitimate son Nikolai (now the king of Ravka), when the rulers of Fjerda get their hands on the letters and use it to try to get Nikolai removed in favour of a cousin of former king Alexander who is more friendly towards Fjerda.
- Implied Trope in The Purloined Letter—probably the contents of the eponymous letter that would so embarrass the royal from whom it was stolen. We never get confirmation of the letter's contents, though.
- Sherlock Holmes
- A Revenge version is the entire premise of the story "A Scandal in Bohemia"—Irene Adler is threatening to send a letter and photo from their affair to her ex-lover's new in-laws.
- A Blackmail version: Charles Augustus Milverton specializes in paying large amounts of money to servants in exchange for such letters, then demanding huge amounts of money from the people involved (mostly women) to prevent the incriminating letters being sent to the husbands.
- In Something New by P. G. Wodehouse, the Honorable Freddie Threepwood, son of the Earl of Emsworth, has just gotten engaged to a rich, beautiful, American heiress, when a friend of his, also engaged, gets sued by another woman for breach of promise because of some old letters. Freddie remembers that he once sent love-letters to a chorus girl, Joan Valentine, and there's a danger she might suddenly pop up and sue him. He sends someone to see if he can buy the letters back, and gets word that the letters have long since been destroyed. So, he relaxes, until his fianceé shows up a few days later with a new maid in tow... Joan Valentine! Quite by coincidence, but Freddie doesn't know that, and assumes he's about to be blackmailed.
- In the Return to Ostagar expansion of Dragon Age: Origins, you can find in King Cailan's camp letters between him and Empress Celene of Orlais revealing that he plans to divorce his wife Anora and marry her. If you have Loghain, Anora's father, in the party when you find this he's incensed by this and calls them, respectively, a "cheating bastard" and "bitch."
- In the HITMAN (2016) mission The World Of Tomotrow 47 can find a love letter to Francesca De Santis from her lover Roberto. Her being an assassination target, 47 can use this knowledge to set up a fake rendezvous with a poisonous surprise.
- In Weregeek Mark's girlfriend found the emails his and Sarah's Vampire the Masquerade LARP characters exchanged and failed to understand that it was just part of a game to him, causing the end of their relationship.
- In the infamous Avatar: The Last Airbender comic How I Became Yours, Zuko's Unwanted Spouse Mai finds out that he has been cheating on her with Katara and that she's pregnant with his kid by finding Katara's letters to him. She then hides the letters to keep Zuko from finding out and sends Katara a basket with poisoned fruits; Katara eats some and ends up having a Convenient Miscarriage. Oh, and in the end Zuko finds the letters anyway.
- A Paternity example in The Simpsons: In "Homer's Paternity Coot", a frozen mailman is discovered and his letters are finally delivered; one of them is a letter from a Mason Fairbanks, whom Homer's mother Mona cheated with, causing him to doubt if Abe really is his father.
- During The American Civil War, Confederate office J.E.B. Stuart once captured a Union officer's trunk and discovered within it "touching letters from a wife, and obscene ones from a mistress" and Stuart proceeded to send all of the letters to the officer's unknowing wife. "They'll be a fuss in that family" commented Stuart's father-in-law Lieutenant Colonel Philip St. George Cooke.
- Poets are dramatic. Elizabeth Ellet liked Edgar Allan Poe, while he liked Frances Osgood. So jealous Ellet threatened to blackmail Osgood with her flirtatious letters with Poe. She was also sending him letters... which he just sent back—she was an Abhorrent Admirer to him. Ellet turned that into a fair bit of drama.