| Errors | Missing | Unverified | Supported |
|---|---|---|---|
| 2 | 1 | 0 | 3 |
In Dial M for Murder, the raincoat swap is a trap orchestrated by Inspector Hubbard to force Tony Wendice to reveal his knowledge of the hidden key. Hubbard swaps his own raincoat with Tony's, ensuring Tony leaves the apartment with the wrong coat (and thus without his own latchkey). When Tony returns and finds he cannot open the door with the key in his pocket (or lacks a key entirely), and knowing the key in Margot's handbag (which he has just retrieved) does not fit the lock, he is forced to use the only other entry method he knows: the key hidden under the stair carpet. By retrieving this key, Tony proves he knew of its hiding place, confirming he was the mastermind behind the murder plot. Crucially, Tony was forced into this position because of an earlier error: he had assumed the key found on Swann's body was Margot's, not realizing Swann had deviated from the plan and returned Margot's key to the hiding spot before entering the apartment.
In Alfred Hitchcock’s Dial M for Murder, the swap of the raincoats (and more specifically, the contents of their pockets) is the pivotal plot device that breaks Tony Wendice’s "perfect" alibi and leads to his ultimate downfall.
The significance of the raincoat swap lies in the logistics of the apartment key, which serves as the film’s central "MacGuffin" and the evidence of Tony’s guilt.
Here is the specific breakdown of its significance:
Tony’s plan involved stealing his wife Margot’s latchkey from her handbag and hiding it under the stair carpet outside their apartment for the assassin (Swann/Lesgate) to find. After Margot kills Swann in self-defense, Tony returns home and realizes he needs to frame Margot.
He takes a key out of the dead Swann’s pocket and places it back into Margot’s handbag, intending to prove that Margot let Swann in (implying they were lovers) rather than Swann breaking in. However, Tony makes a fatal error: The key he took from Swann’s pocket was not Margot’s key; it was Swann’s own latchkey to his own home. Swann had put the apartment key back under the stair carpet after entering, just as Tony had instructed.
Chief Inspector Hubbard becomes suspicious when he realizes that Margot’s handbag (which was seized as evidence) contains a key that does not fit the Wendices' door. He eventually finds the correct key hidden under the stair carpet.
To prove Tony’s involvement, Hubbard realizes he needs to catch Tony in the act of demonstrating knowledge of that hidden key.
The raincoat swap occurs near the end of the film. Hubbard orchestrates a scenario where Tony is separated from his raincoat.
Because Tony cannot get into the apartment with the key in "his" pocket, and he knows Margot’s key is supposedly in her handbag at the police station, he is forced to look for an alternative.
Thinking he is alone and unobserved, Tony remembers the original plan. He walks up the stairs and reaches under the carpet to retrieve the hidden key. When he uses that key to open the door and walks into the room, he finds Inspector Hubbard, Margot, and her lover Mark Halliday waiting for him.
The summary fails to note that Swann *deviated* from the plan by returning the key early. This is crucial because if Swann had followed instructions, the key would have been in his pocket, and Tony's assumption would have been correct.