- A crime is commited.
- A detective (or some other appropriate character) starts investigating the crime.
- She comes across a very obvious suspect: someone who seems to have had the motive and means to commit the crime.
- But she then discovers the obvious suspect couldn't have done it. Maybe the suspect has an alibi, or he can otherwise be ruled out. For example, someone has been murdered, and the forensic evidence reveals the killer was right-handed. The obvious suspect, however, turns out to be left-handed.
- The detective then finds out the real culprit was someone unexpected. For example, it can be someone who seemingly didn't have any reason to commit the crime, until the detective uncovers said reason.
This plot formula is typically used in fair-play whodunnits and other types of mysteries where there are several suspects. The obvious suspect functions as a Red Herring, and the story often culminates with The Summation, where the unexpected culprit and the reason why he committed the crime are revealed.
Writers like to use the above formula because it adds a twist to the story. Discovering the culprit becomes an interesting puzzle instead of the detective simply finding the number one suspect and arresting him. However, this trope has become so common that the audience is now used to it, which means they pretty much expect the real culprit to be someone else than the obvious choice. In most cases, the twist is also Spoiled by the Format: if a detective show lasts for 45 minutes, and after the first 15 minutes the detective already appears to have caught the guilty party, it's almost certain the real culprit will turn out to be someone else.
Sometimes the writers like to play with audience expectations and subvert the trope as a Meta Twist by having the detective dismiss the most obvious suspect and go through others, only to discover later on that the person she originally suspected was guilty after all. This is usually accompanied by some kind of unexpected reveal that explains how the obvious suspect was able to appear innocent. To use the example above, if the murder was commited by a right-handed person, and the detective rules out the obvious suspect because he's a leftie, she may later discover that he's ambidextrous, so he was the murderer after all. Subverted Suspicion Aesop is another plot formula where someone who appears to be guilty really is so.
Since this trope deals with plot twists and surprise revelations, the examples below may contain spoilers!
- Subverted in an early John Byrne Superman story, Scotland Yard comes to see Superman for helping finding Winn Schott aka the Toyman. They relate how they've been following him after a murder spree against the toy company owners who fired him, often using his own toy designs. A baffled Superman asks why they didn't just go after Schott in the first place when the evidence was clear. With some embarrassment, the inspector admits that he and his team were so used to cases where the least likely suspect was the killer that it took a while before they realized it really was the most obvious person.
- Played for Laughs in A Shot in the Dark. Clueless Detective Clouseau ignores blatant evidence that the woman he's infatuated with is the killer, even though she keeps being found standing over a victim, holding the murder weapon, with no idea of what happened. Of course everyone except her turns out to be a murderer.
- Agatha Christie used this trope in various ways.
- Subverted in The Mysterious Affair at Styles. The murderer deliberately makes himself the very obvious first suspect, then prepares provably fake evidence, so the case against him will be overturned and he won't be suspected again (in English law at the time, one couldn't be tried twice for the same crime).
- Subverted in The Hollow. The guilty party is standing near the shot man’s body with a pistol in her hand. Yes, just like that. She really is the one and only perpetrator.
- Subverted in Lord Edgware Dies. The criminal knew everyone was bound to suspect her, and took great pains in establishing a solid alibi, thanks to the help of a double, and demonstrating a seeming absence of motive. While in fact, everything happens just as everyone thinks: she walks into Lord Edgware’s house and stabs him.
- Lampshaded in Peril at End House. When Hastings dismisses a suspect on account on him being too suspicious to be guilty, Poirot says that while the least obvious guy is usually guilty in books, in real life, the most suspicious-looking one is usually the criminal. The ending, though, plays it completely straight, as the murderess has been posing as the intended victim the entire time.
- Zig-zagged generously in Murder on the Orient Express. The more obvious and the less obvious ones – all turn out to be murderers in the end... that is, except for Poirot, his friend, the doctor – and the one who was the first and the most obvious suspect to be discovered: Countess Andrenyi knew of the crime, but was asleep while it was being committed.
- Occasionally referenced by Tommy and Tuppence in Partners in Crime as part of their Conversational Troping of mystery tropes. for instance, in one story Tommy jokingly suggests the criminal is a woman in a wheelchair with no perceivable motive, because she's clearly the least likely suspect. In another Tuppence is disappointed that other evidence seems to rule out the wife, because she always suspects wives who were nowhere near the scene of the crime and couldn't possibly have done it.
- Harry Potter:
- Severus Snape is a sly, abusive teacher who has a clear affinity for the Dark Arts throughout Harry Potter and the Philosopher's Stone. It turns out that Snape is not only not the antagonist, he is actively protecting Harry from the antagonist.
- Draco Malfoy is a schoolyard bully who vocally supports the actions of the mysterious Heir of Slytherin in Harry Potter and the Chamber of Secrets. Harry and co. spend months investigating the connection between the two, but it becomes obvious Draco has nothing to do with the Heir.
- Harry Potter and the Half-Blood Prince sees Harry suspect Snape and Malfoy yet again, this time of hatching several failed assassination plots from within Hogwarts. By this point, Harry's friends and allies are Genre Savvy enough to attribute his suspicion to his dislike for both people. As it turns out, Harry is completely right about both, even if their situations are much more complex than Harry assumed.
- Angels & Demons sees a plot to exterminate the Vatican with an antimatter bomb. The brains behind the attack remain hidden until the novel's end, but that doesn't stop Professor Langdon of suspecting Maximilian Kohler, a vocally anti-religious scientist who helped fund the antimatter bomb to begin with.
- Parodied in The Macbeth Murder Mystery by James Thurber, in which a detective novel fan reads Macbeth and decides that Macbeth, being the obvious suspect, must be a Red Herring and thus that King Duncan was killed by someone else.
- Lord Peter Wimsey:
- Played straight in Strong Poison, where Harriet is the obvious suspect in the poisoning of Philip Boyes - so much so that the story starts with a judge summing up the evidence for the jury at Harriet's trial. After the jury returns a hung verdict, Lord Peter has thirty days to prove that Harriet didn't do it.
- Discussed in Busman's Honeymoon, just before interviewing the last person to see the victim alive:
Lord Peter: Enter the obvious suspect.
Harriet: The obvious suspect is always innocent.
Superintendent Kirk: In books, my lady.
- Conversational Subverting in The Five Red Herrings, where Lord Peter says that if he wrote a detective story it would open with a man with a gun fleeing a cul-de-sac containing a dead body and nobody else, and 20 chapters "stinking with red herrings" later, it would turn out he was the murderer.
- In The Rithmatist, there's Professor Nalizar, who is much like Snape- a nasty, arrogant teacher who the protagonist Joel immediately suspects of being involved in the evil doings aroud the school. Eventually, Joel discovers that Nalizar was not the one who caused the disappearances and admits that Nalizar was a hero who saved his life- but in a subversion and something of an invocation of the trope, Joel then finds out that Nalizar was behind it all, and he gloats that, since Joel had already recanted his suspicions, he can't credibly accuse him again.
- In Magical Girl Raising Project Restart, the goal of the players is to kill the Evil King hiding among them, whose goal is to eliminate the other players. Melville murders several of them in secret over the course of the game, and she has connections to a former villain, so naturally she must be the Evil King. Except she is just another player, and the real Evil King is Nokko, who never took direct action against everyone and was always cooperative, opting to manipulate them with her Emotion Control powers instead.
- Most episodes of iZombie follow this formula, though it gets occasionally subverted when the obvious suspect is revealed to be the killer after all (such as in the episode "Brother, Can You Spare a Brain?").
- Elementary often uses this trope, unlike the Sherlock Holmes stories the series is loosely based on.
- Gotham deals with the origins of various Batman villains and as such it is only a matter of time before The Joker is introduced. Enter Jerome, a Laughing Mad circus freak who murdered his own mother, who imitates the mannerisms of Heath Ledger and Mark Hamill. As "The Last Laugh" shows, the Joker is someone else entirely.
- Shawn from Psych has had a few of these. One example is Emily Bloom from "Black and Tan: A Crime of Fashion". After her bosses (husband and wife fashion moguls) are murdered, she gets fingered as the prime suspect. She had motive (the wife was verbally abusive to her, the husband stole her designs, and she was next in line for company president), means (she made the wife's protein shake which contained the poison that killed her), and gives O'Hara a makeover when she comes to interrogate her (read: bribe). Not only is Bloom not the killer (the couple actually killed each other), she's almost the next victim when she accidentally drinks a poisoned shake.
- Star Trek: The Original Series. In "Wolf in the Fold", Scotty is found on three separate occasions standing over the corpse of an attractive woman with blood on his hands and no idea of what happened. Captain Kirk uses Insane Troll Logic to argue that the ghost of Jack the Ripper is responsible. He's right, of course.
- In the Star Trek: Deep Space Nine episode "The Passenger", a bad guy named Vantika escapes the death of his body by transplanting his mind to another person. The most obvious target for this mind transfer is Kajada, who becomes the main suspect because of this. But then it turns out Vantika actually resides in the brain of Bashir, whom none of the protagonists suspected, even though most viewers had probably guessed it long ago due to a very obvious hint dropped in the first act.
- Hunter would always play this straight, except one episode that did the Bait-and-Switch. A woman dies during a gang rape, with the culprits let off on a technicality. When they are shot one by one, the victim's sister is the obvious suspect. Then it looks like a Corrupt Corporate Executive has a motive, and she's being framed as a patsy. Nope, it was the sister all along.
- This is a standard part of the average Soap Opera murder mystery, where the first person arrested for killing the Asshole Victim inevitably turns out to be innocent, despite him/her having had a HELL of a motive/means/opportunity. Port Charles went for The Un-Twist when the prime suspect in the so-called "General Homicide" turned out to be exactly who all the evidence had pointed to.
- Played straight in all but two trial cases in the Ace Attorney games (including the crossover with Professor Layton), where the culprit is not the defendant. Given that the entire premise of the series is of a defense attorney trying to clear his clients of murder charges, the real application of this trope should be when Phoenix's first suspect isn't the guilty one, which happens a couple times as well (most famously, in the final case of Justice For All, Phoenix accuses someone, only to later discover the real killer was hired by the defendant himself.)
- Parodied in Bob's Burgers: When Linda performs a stage play in the restaurant, Louise plays a butler who reacts dismissive to the murders and loudly remarks that the murder weapon is hers. This is intended as a (lazy) Red Herring, with Linda actually being the killer. When the true killer is revealed, the audience becomes angry since clearly The Butler Did It and there were no clues pointing to Linda.
- Archer: In "Skytanic", when investigating a bomb threat on a zeppelin, Archer at first suggests the German second mate, Kraus, who has a sinister-looking scar emanating from under an eyepatch, but then immediately dismisses him as "too obvious" and moves on to a man in a (Sikh) turban. Turns out Mallory faked the bomb threat to get free tickets, but Captain Lammers coincidentally planted a real bomb (whether he did this independently or because of the bomb threat is unknown) with the intention of shorting the stock and recouping his retirement fund. Kraus knows how to disarm the bomb and also received the scar while saving a Jewish girl from a gang of skinheads who threw him a "curb party" for his efforts. He is unceremoniously shot by Lammers before he can disable the bomb.