Wayne Dobie is a shy cop whose low-key demeanor has earned him the affectionate nickname "Mad Dog." After Mad Dog saves the life of Frank Milo, a crime boss and aspiring stand-up comedian, he's offered the company of an attractive young waitress named Glory for a week. At first both are uneasy about the arrangement, but they eventually fall in love. However, the situation becomes complicated when Milo demands Glory back.

A spate of killings of teenagers by a maniac dressed like a hippie causes a detective to check the records for similar killings. He discovers that every five years, in the fifth month of the year, for five consecutive days, the same type of killings have occurred, and the few descriptions of the suspect always match: he's dressed like a hippie. As the detective searches for the killer, he begins to have suspicions about his superior, an older man who is haunted by memories of his military service in Vietnam.