Dave Garland (Clint Eastwood) is a Californian DJ who runs a late night call-in show, and receives regular requests from a female caller for Erroll Garner's 'Misty'. Following a bust-up with his regular girlfriend, Tobie (Donna Mills), Dave has a one-night stand with Evelyn Draper (Jessica Walter) after meeting her at his regular night spot. It transpires that Evelyn is the mystery caller on Dave's show, but after their night together she becomes obsessed with him, refusing to accept his subsequent rapprochement with Tobie. Evelyn's rage at first takes a suicidal turn, then becomes murderous as she makes violent threats towards Dave and Tobie.