On the surface, Richard (Humphrey Bogart) and Kathryn Mason (Rose Hobart) appear to be a happily married couple. But on their fifth wedding anniversary, Kathryn accuses Richard of having fallen in love with her younger sister, Evelyn Turner (Alexis Smith), who is visiting them. He does not deny it, but has resigned himself to leaving things as they are, since Kathryn certainly would not give him a divorce. At a party celebrating the couple's anniversary, hosted by family friend and psychologist Dr. Mark Hamilton (Sydney Greenstreet), Evelyn meets with Mark's handsome young colleague, Professor Norman Holdsworth (Charles Drake (actor)). On the way home, Kathryn suggests to Evelyn that their mother is lonely, so Evelyn decides to move back home. Distracted by this unwelcome news, Richard crashes their car and suffers a broken leg.