Whitney Cameron (Joseph Cotten) is in a quandary: he's attracted to his beautiful sister-in-law, Lynn (Jean Peters), but also harbors serious suspicions about her. Her husband, Cameron's brother, died under mysterious circumstances, and now that the death of her stepchild, Polly, has been attributed to poisoning, he suspects that Lynn is after his late brother's estate, and killing everyone in her way. Cameron fears that nephew could be next, and determines to make sure no harm comes to him.