After learning that his wife Margot (Grace Kelly) had an affair with a mystery writer, Tony Wendice (Ray Milliant) decides that divorce isn't enough: he's going to kill her.
He wants to provide himself with an ironclad alibi – so he blackmails a one-time schoolmate with a shady past into doing the killing for him. But there's no such thing as a perfect crime, and his machinations do not go as planned.