Paul Steppe, a successful watchmaker, begins to suspect that his wife Fran is seeing another man. Consumed with jealousy, Steppe decides to murder her. His plan, he feels is ingenious. Painstakingly Steppe applies all of his watchmaking skills to the construction of a time bomb. He plans to slip into his house in the afternoon without his wife's knowledge, leave the bomb and then return to his jewelry store unnoticed and unsuspected.