Ex-Tennis Player Tony Wendice (played by Ray Milland) discovers his wife Margot (played by Grace Kelly) is having a love affair with the American Crime Fiction Writer Mark Halliday (played by Robert Cummings). In a fury of anger and greed, Tony comes up with an intricate plan to murder his wife and get all her money by influencing an old colleague to perform the deed (Charles Swann played by Anthony Dawson). While she is home alone, Tony's plan goes awry when she kills Charles in self defense. However, by tampering with the crime scene, Tony makes it look like Charles was blackmailing Margot for her love affair and she murdered him in cold-blood. Will Mark be able to prove Margot's innocence to the local police inspector or will she be falsely executed by the court of law?
In this film, Hitchcock creates suspense by informing the audience of how the murder should go before it actually happens. Using anticipation, we cannot relax as we already know how the murder should go down. But as the scheme unfolds, we are surprised by unexpected elements that are interjected causing a disruption to the projected murder plan. Knowing this, even though Hitchcock masterfully tells this story, it can be quite confusing without plotting it out. So, using lessons I've learned while working on my Master's degree, I will be using a Systems Engineering Approach to better observe how this story unfolds.
Mapping out events is a great way to analyze and solve complex problems. In this film, the murder plot was both ruined and solved by 3 different keys (meaning the objects that unlock doors) which traveled between characters. Using a relationship diagram, here was the route of the 3 different keys distinguished by 3 different colored arrows:
There were only 2 keys that opened the Wendices' apartment, one belonging to Tony, the other to Margot. The blue arrows symbolize the path of Margot's key:
- Tony obtains Margot's Key
- Tony hides the key under the stairs for Charles
- Charles takes the key to open the apartment
- Charles places the key back under the stairs
- Tony later figures out Charles put the key back under the stairs, opens the door, and is caught for knowing the hiding spot
The green arrows symbolize the path of Tony's key (this is the other key that can unlock the apartment):
- After Charles is killed, Tony removes a key from his corpse, mistaking it for Margot's
- Tony returns the false key into Margot's purse
- After Margot is imprisoned, the Inspector confiscates the false key
- After the Inspector discovers the key cannot open the apartment, he switches the key for Tony's original
- Tony tries to unlock the apartment, realizes it's false, and is caught for opening the door with the right key hidden under the stairs
- Tony puts his original key in his coat pocket while talking to the Inspector
- Unknown to Tony's knowledge, the Inspector switches the actual key with the false one, using it to prove Margot's innocence
So on Death List Five, Dial M for Murder Ranks #4.