Every Saturday evening, travelling salesman Ferdinand Ravinel returns to his wife, Mireille, who waits patiently for him at home. But Ferdinand has another lover, Lucienne, an ambitious doctor, and together the adulterers have devised a murderous plan.
Drugging Mireille, the pair drown her in a bathtub, but in the morning, before the "accidental" death can be discovered, the corpse is gone--so begins the unraveling of Ferdinand's plot, and his sanity...