Widow Helen Gordon (Ida Lupino) hires Howard Wilton (Robert Ryan) to do some odd jobs around her large Victorian mansion. What she doesn't know is that Wilton is actually a murderous schizophrenic prone to violent blackouts. Although he has no memory of it, Wilton killed his last employer, and when his grip on his sanity begins to slip away while working at Helen's house, she has to think on her feet to keep him calm and rational until she can escape from her home and get help.