After Tony Wendice (Ray Milland) finds out that his wife Margot (Grace Kelly) is in love with another man Mark (Robert Cummings), Tony decides to murder Margot. First, he makes himself the beneficiary of Margot's estate. Then, he hires a criminal named Swann (Anthony Dawson) to kill Margot. On the night of the murder, Tony takes Mark to a party to give himself an alibi. Unfortunately, things go wrong with the murder because Margot fights back and ends up killing Swann. Tony attempts to cover up his involvement in the attempted murder of his wife, however Mark is suspicious, and the Inspector (John Williams) is suspicious that something is going on.