Helen, a race-car driver whose life, both personal and professional, is in a rapid downfall, is invited by her ex-husband's new wife Constance to stay at their plush estate. The two women form a bond, and it's not long before their mutual dislike for the husband culminates into a plan to kill him. Their plan to murder Maurice on a sailing trip goes awry, and Constance is accidentally killed instead. Helen and her ex seize the moment and dispose of Constance's corpse at sea, but when the dead woman's daughter Susan arrives, the young lady begins to suspect that her mother has been murdered.