Basic Trope: Two characters with motives to kill someone in their lives meet by chance, and enter into a deal to 'swap' murders so as to avoid suspicion for killing the person they have a motive to kill.
- Straight: Bob and Charlie meet by chance on a train. Bob has a grudge against his ex-wife Alice, whereas Charlie resents his uncle Duncan. During their conversation, Bob offers to murder Duncan for Charlie if Charlie will murder Alice for him.
- Exaggerated:
- Bob and Charlie make a complete list of everyone they have a motive to murder, and agree to murder everyone the other hates.
- Bob, Charlie, Alice, Jim, Slim, Archibald and fifty more of their collective friends band together to switch crimes (not all of them murders, but still potentially life-sentencing).
- Downplayed:
- Bob and Charlie both agree to do something nonlethal to Duncan and Alice respectively.
- Bob and Charlie decide to exchange information of their companies and game the stock exchange without being suspected of insider trading.
- Justified: Bob believes that Charlie, a complete stranger to him, will never be suspected for murdering someone he has never met, and vice versa; they will commit the 'perfect' murder.
- Inverted:
- Bob and Charlie, who have never before met, join forces to discover who is murdering people close to them and trying to frame them.
- Bob's going to propose to his fiancée, but doesn't want her to suspect it's him. Charlie wants to leave a surprise gift for his hard-working uncle. Bob and Charlie team up to do these nice deeds for each other.
- Subverted:
- Bob and Charlie make a pact, but both get cold feet and decide not to go through with it.
- Charlie is a cop.
- Bob and Charlie discuss what kind of crimes they could perform with their alleged perfect alibi, before agreeing that they don't have the stomach for murder and decide to do something less nasty like insider trading.
- Bob and Charlie had fictional targets and agreed to a Revenge Fic Story Swap.
- Double Subverted:
- Only Charlie gets cold feet, but he assumes Bob has; Bob, in fact, hasn't, and murders Duncan with the expectation that Charlie will now kill Alice for him.
- Charlie is a Dirty Cop, this isn't a sting.
- Things go bad for their so-called "less nasty crime", so they end committing murder anyway. And a dozen more crimes, including more murders, to cover up the first.
- Parodied:
- Unfortunately for them, neither Bob nor Charlie are actually that competent at trying to murder someone, and make numerous attempts with increasing frustration at their failures. This results in them frequently meeting up to lick their wounds and commiserate with each other.
- Bob and Charlie meets in a "Speed Homicide Switch" Pub, where everyone goes to find a dilettante killer with a target on his own.
- Zig Zagged: After planning crossed homicides, both waits for the other to be the first, to the point that the homicides are aborted. Then they agree to give a serious try both on the same target, once at a time, but during the first attempt, they acknowledge that this would attract suspicious. So they abort again, but while chatting about the original reasons to kill the targets, each agrees that the other's target deserves to die. So the original plan is restarted, but before they can put it in motion they find out that everyone else noticed their newborn friendship, and it burst the whole alibi business.
- Averted: Neither Bob nor Charlie make plans to murder each other's preferred victim. Or even meet up at all.
- Enforced: "Wasn't Strangers on a Train a great movie? We should totally do a Mystery of the Week plot based on that."
- Lampshaded: During their meeting, Charlie notes how similar the plot Bob is approaching him with is to Strangers on a Train.
- Invoked: Bob is intentionally seeking out someone with a motive to kill someone close to them in order to carry out his plan, and has been 'casually' scoping people out for months.
- Exploited:
- A fifth person, Emily, hates Alice and Duncan. She puts Bob and Charlie together on purpose in the hopes that they'll make this kind of agreement.
- Police set up sting operations to catch people making such agreements. Even if most really are legitimate third parties seeking murder swaps undermining trust in random strangers accomplishes the mission anyway.
- Defied:
- "You're suggesting we commit a murder based on a movie? That's ridiculous, and I'm not having any part of it."
- Bob and Charlie would both rather do their own dirty work and personally murder the people they hold grudges against.
- Discussed: Police inspector, after the murders, "Weren't Charlie and Bob on a train together recently? Maybe they made a deal."
- Conversed: "Dude, didn't they get caught in that movie?" "... Our plan will be better."
- Deconstructed: Bob and Charlie's plan is unfortunately flawed in that the police are nevertheless able to establish connections between them and the murders they do commit. Furthermore, motive isn't the sole factor that the police examine when investigating the crime. The police are able to establish connections between Bob and Charlie and successfully prove their plan, and both are arrested.
- Reconstructed: Though neither Bob nor Charlie make a pact, they are each moved by the depths of the other's frustration to commit the murder the other is not willing to do.
- Implied: Bob and Charlie gripe to each other about Alice and Duncan, and it seems they both might resort to murder. The next day, both of them turn up dead, but Bob is cleared of suspicion for Alice, while Charlie is cleared of suspicion for Duncan.
Back to "Strangers on a Train"-Plot Murder... say, with your uncle and my ex-wife, it seems like we both have people in our lives we could do without... fancy a swap?
