When FBI Agent Zack Stewart is killed, Agent John Ripley takes over the three cases he was working on, hoping one will lead to his killer       The first involves gangster Joe Walpo and Ripley finds his hideout through Joe's girl friend, Connie Anderson       Joe is killed but it is established he was 400 miles away when Stewart was murdered       The next involves a car-theft gang which Ripley breaks up by using one of the gang, Vince Angelino and his wife Julie       The last case involves Kate Martell, the victim of an extortionist who threatens to kidnap her child unless she pays him $10,000