Country squire, Henry Maurier (Charles Boyer), is regarded as a saint for putting up with his neurotic, invalid wife Emily (Rachel Kempson). But when Emily's brother visits them with his voluptuous mistress, Doris (Ann Blyth), the ageing squire falls instantly in love with the young temptress. That very night Emily dies suddenly of chronic heart disease, and Henry is left free to seduce and later marry Doris - much to the annoyance of their neighbour, Janet (Jessica Tandy) who has secretly loved Henry for many years. When a post-mortem shows that Emily's death was precipitated by arsenic, Henry is arrested for murder and placed on trial for his life. But is he guilty?