Oh, hello there. I didn't see you. I was too busy thinking about my horrible father — but you don't want to hear about it. You probably have troubles of your own. Perhaps a shrill ex-wife? And you don't want to pay her alimony any more, you say? Well, perhaps we met for a reason. Listen: I'll "X" your ex, if you pop my pop. Ah, I knew this was a good idea. We'll each have alibis for the other crime, and we won't have apparent motives for the one we did commit. It's perfect we'll never get caught.
A non-lethal version of the trope exists on sitcoms, in which two characters who can't bring themselves to tell loved ones something that will hurt them will swap duties thinking it will be less painful coming from the other character. A similarly non-lethal (or at least "non-lethal" at first) variation is people exploiting their apparent lack of connection to get alibis for crimes like insider trading. Another variation can come in Villain Team-Ups where the villains in question belong to two separate heroes' Rogues Galleries.
Compare with "Gift of the Magi" Plot, where two characters plot to give each other a gift that is nullified by the sacrifice the other did to get them a gift.
- Detective Conan has a filler episode in which this is used as the plot.
- Non-murder example: In Operation P.O.W.E.R.P.U.F.F., Mojo Jojo and the Delightful Children pull this with Mojo Jojo kidnapping Numbah Three, and the Delightful Children kidnapping Ms. Keane. Mojo Jojo even points out the trope maker when he reveals the plan.
- In Ace Attorney fanfic Dirty Sympathy it's the basis of the plot, it is also a non-murder example as they chose to frame their tormentors instead of killing them with Klavier framing Apollo's Bad Boss Kristoph and Apollo framing Klavier's boyfriend Daryan. Apollo doesn't agree to it at first until Kristoph threatens to kill him. He becomes a lot more receptive to filling his end of the deal after Kristoph is sent to jail and they stop being strangers.
- Alfred Hitchcock's Strangers on a Train. It was probably Adaptation Displacement for Patricia Highsmith's book, too. Interestingly, it isn't a straight example - Guy doesn't agree to the murder swap and doesn't go through with killing Bruno's father.
- Throw Momma from the Train: A homage, parody and eventual subversion of Strangers on a Train.
- Horrible Bosses name-checks both the above movies. Of course, they miss the important points that they shouldn't know each other, and they should have alibis when the other murders happen.
- Happens in the British film Sweet Revenge, an adaptation of the play The Revengers' Comedies. Henry Bell and Karen Knightly strike a bargain for the murders of Henry's boss and Karen's lover's wife. Subverted in that Henry finds himself falling in love with his target.
- The Strange Vice Of Mrs Ward. They also employ a third accomplice.
- The 1994 straight-to-video movie Dead On. Adulterous lovers Ted and Erin agree to kill each other's spouses. After Ted's wife Marla disappears, he murders Erin's husband... and becomes a suspect in the murder after the affair comes to light. It turns out his wife's body wasn't found for a good reason - Marla is still alive. It was actually a plot between Marla and Erin to get rid of each other's husbands, so that Erin becomes a wealthy widow, and Marla (who was already rich) gets to divorce Ted without alimony after he's sent to jail for the murder. Knowing he's going to jail anyway, Ted pulls a Taking You with Me and kills them both. They really should have checked him for a gun before they pulled their gloating reveal.
- The Trope Maker, Patricia Highsmith's novel Strangers on a Train, also isn't quite a straight example. From the start, Guy Haines explicitly refuses to be part of Charlie Bruno's plot, and leaves him to find somebody else. Unfortunately, Bruno is fond of Haines, and kills his wife anyway as a favor. Then he starts stalking Haines to try and make him follow through with his end of the "bargain". Unlike in the Hitchcock movie, Haines becomes so demoralized that he does kill Bruno's father. The plot is eventually found out by the police, in large part because Bruno ignores the "strangers" bit and starts wedging himself into Haines's personal life.
- One of the Eve Dallas novels, Strangers in Death.
- The Shadow Club begins as the PG version of this, with various bullied teens exchanging pranks. Then someone begins to commit more serious misdeeds, some of them dangerous, and none of them are sure who's gone too far. Everyone except the narrator did one and only one of the serious misdeeds on the unknowing behalf of one other club member they cared deeply about. The narrator winds up accepting guilt for his girlfriend's "prank," which permanently crippled a Jerk Jock.
- Done in a fairly easy Clue tie-in mystery book. There are three failed attempts at murder, in each case two people with motive are missing. Since one was missing on all three occasions, the two killers are obvious.
- In A Pen-Knife in My Heart, a novel written by future Poet Laureate Cecil Day-Lewis under his Nicholas Blake pen name, Stuart Hammer takes weak-willed author Ned Stowe out on his boat and makes him a proposal. Stuart will kill Ned's wife so that Ned can be with his mistress Laura. In return Ned will murder Stuart's uncle, who's also his boss. Published eight years after Strangers on a Train and six years after Alfred Hitchcock's movie, the plot was close enough so that Day-Lewis had to make some last minute changes in order to avoid a lawsuit from Highsmith's publisher.
- In the short story "Strangers On a Handball Court"by Lawrence Block, two men exchange their ex-wives' murders. One of them conceals the fact that he is still married to the target and having an affair with the second man's wife. He then kills the "stranger" who broke into his house and murdered his wife.
- Used as a plot point in Death Will Attend, the second book in the Caching Out-series by Morgan C Talbot.
- In the Castle episode "The Double Down," it was Strangers on a Boat. Castle even does the "criss cross" gesture. As a writer, he is understandably excited.
- In the episode "The Inside Man", it was Strangers on a Commuter Train... although the crime was insider trading rather than murder, at least to start with.
- The episode "Alibi" has this with Strangers at an AA Meeting. In fact, the suspect in a hit-and-run tries to alibi out to his attorney by explaining that he was stabbing a guy to death in another town during the hit-and-run, and she can't tell anyone due to the attorney-client privilege (she still finds a way to leave a hint for Gibbs).
- In an episode of CSI, it was Strangers in a Movie Theatre (coincidentally watching Strangers on a Train). Someone even points out how well that plot worked in the film (i.e. it didn't).
- Heartbeat. Local rogue Claude Greengrass has just been to see the movie Strangers on a Train and jokes loudly afterward about how he's like someone to burn down his old barn for the insurance money. Unfortunately, someone takes him at his word, and gets nasty when Claude doesn't keep his side of the 'bargain'.
- Bones did a three way "Strangers on the Internet" version of this once in "The Bodies in the Book".
- In the Modern Family episode "Strangers on a Treadmill", Mitchell suggests to Claire that he tell Phil his jokes are rotten while she tells Cam that he shouldn't wear embarrassingly revealing bicycle pants.
- An episode of Supertrain did a literal "Strangers on a Train" homage with Dick Van Dyke as the psycho.
- Dick Van Dyke subverted this trope in an episode of Diagnosis: Murder. A deranged psychiatrist killed a hospital administrator who was going to recommend that Dr. Sloan(Van Dyke) be dismissed from Community General when he protested her bone-deep budget cut recommendations. The psychiatrist then called up Dr. Sloan and told him, "Now you owe me a favor." Dr. Sloan refused to play along.
- Series two of Psychoville features a parody/homage of "Strangers on a Train." David agrees to kill Mrs Wren so that her nephew can inherit her money, with the nephew agreeing to "relieve Maureen of her pain" (she is dying of cancer) in exchange; they meet on a train to discuss the plan. It backfires when Jelly escapes with the real Mrs Wren, leading to her roommate (who was wearing a borrowed cardigan with Mrs Wren's name sewn into it) being mistaken for her and murdered by Finney, and David finding the body. Meanwhile, Maureen catches Wren's nephew breaking into her house, and kills him - then discovers he wasn't planning to murder her, he was there to give her a disabled parking badge.
- The Closer has a non-murder (at least initially) variation. A group of teenagers whose parents are all well-off make a plan: each time one of them goes on vacation with their family, the rest of the group will break into their house and steal laptops and stuff, because they figure that they want stuff, and since their parents are rich they can just replace the missing things. It backfires when one of them decides he doesn't want to do it any more, but the others decide to break into his house anyway when he and his parents go on vacation, and accidentally kill the house-sitter.
- Criminal Minds episode "The Pact" has a pair of women who've had a child relative killed by people who escaped justice deal with each other's target this way. Reid quickly figures this out and references the trope namer.
- Done in a Columbo episode "A Friend in Deed", although the perpetrators are not really strangers. They almost manage to get away with it.
- Medium had 5 Strangers On An Airport Lobby combined with Serial Killings, Specific Target: the victims would all be poisoned with the same tainted painkiller, so that the deaths would be blamed on a serial poisoner, since there was no apparent connection between the victims.
- The Silent Witness story "Supernova" is based around this, with teenage girls plotting via the internet to murder people on each other's behalf.
- Done in the Death in Paradise episode "A Dash of Sunshine", although the first murder is not seen; having already taken place in another country.
- Used in an episode of Rizzoli & Isles. Two people, each wanting to be rid of their spouses, meet at a dog park and agree to swap murders. They're careful not to correspond on computer or talk on the phone, being Genre Savvy enough to know they could be traced that way. Dog hair left at one of the murder scenes is what trips them up.
- The Murdoch Mysteries episode "Unfinished Business" has this as a cold case, reopened when one of the conspirators makes a Deathbed Confession, but leaves Murdoch with the impression he killed his own wife, which he can't have done. When Murdoch realises what happened, he even suggests they may have met on some form of public transport.
- Done on The Mysteries Of Laura with a twist: the first murder was committed by neither of the two connected with the plot and the person who agreed to murder the second victim goes through with it to hold up his end of the bargain.
- Motive: The murder in "Undertow" turns out to be a case of this. However, the second man gets cold feet and cannot go through with his part of the bargain.
- Law & Order episode C.O.D. has this with two women conspiring to kill their respective husbands.
- Parodied in Season 2 episode 3 of John Finnemore's Souvenir Programme: Leonard (the Bruno character) knows that Nicholas (the Guy character)'s wife is always nagging him about vacuuming, and explains that his mother is always on about his cat's litter tray. After an increasingly blatant set-up, which includes the phrase "strangers ... on a train" several times, and a cameo by Alfred Hitchcock as the guard, he finally suggests ... they swap chores. While protesting that this is a stupid idea, Nicholas suggests the murder thing, at which Leonard is absolutely horrified. He calls the guard in, demanding that Nicholas be arrested because "He's a psycho and obsessed with my mother!" And that gives Hitchcock an idea...
- The protagonists of Grand Theft Auto V do this in Ending C. However, it's not done for the normal reasons. They do it so that their victims don't recognize them as a threat since they don't know them personally.
- Crash Bandicoot Purple: Ripto's Rampage and Spyro Orange: The Cortex Conspiracy have Ripto and Dr. Cortex take on the other's usual enemy while also trying to set up a Let's You and Him Fight between Spyro and Crash.
- A variation of this is a key part of the plot behind the Dai Gyakuten Saiban duology. The "exchange program" is actually an assassin exchange, where the heads of the English and Japanese judicial systems send an assassin to kill a target in each other's country, and the judicial heads will claim immunity if the assassin is caught, forcing the country to send the assassin back without prosecution.
- Robot Chicken parodied this mercilessly, to the point of Crossing the Line Twice, in a sketch where O.J. Simpson is unwillingly roped into this by Roger Rabbit.
- Played With as part of a Hitchcock parody in the The Simpsons "Treehouse of Horror XX" short Dial 'M' For Murder or Press # to Return to the Main Menu. Bart and Lisa aren't strangers, but they do agree to swap revenge on their teachers... except Lisa only thought they were swapping pranks, while Bart saw it as the classic murder swap.
- Fillmore! had an episode where it looked like a vigilante was going after bullies. It turned out that the victims of various bullies had decided to fight back, but they swapped targets so that each of them would have an alibi when the bully they had reason to hate was targeted.
- The Hercules Crossover episode with Aladdin: The Series had Jafar and Hades try this at first to deal with Herc and Al. Once it became clear that Hercules' strength was enough to overpower Jafar's sorcery and Genie one-shotted Pain and Panic, Jafar suggests a Let's You and Him Fight scenario instead.
- The final episode of the short-lived Gary and Mike, titled "Crisscross", parodied this.
- Brandy & Mr. Whiskers: In "Dog Play Afternoon", Gaspar and Brandy are understudies for the main leads of the play. Gaspar suggests Brandy to play dirty:
Brandy: Come on! If something happens to the stars, It would be obvious we did it!
Gaspar: Ah, what if I took care of your problem, and you take care of my problem. If anyone asks, we both would have alibis. (aside comment) It is a totally original idea, nobody has ever thought to use it in a movie plot.