In this offbeat crime drama, Mafia boss Johnny Colini (Marc Lawrence) has run afoul of the law and is being deported back to his native Sicily. Colini is not at all happy about this, and after he saves the life of a young thug, Johnny Giordano (Henry Silva), he knows the perfect way for Giordano to pay him back. Colini teaches Giordano the fine art of being a hit man, then sends him to America as Johnny Cool, with a long list of people who he believes informed on him to the police. Johnny Cool begins knocking off Colini's old enemies with a brutal violence that betrays the cool detachment of his personality; along the way, he meets Dare Guinness (Elizabeth Montgomery), a beautiful but promiscuous woman with whom Johnny falls in love. Several gangsters wanting to stop Johnny Cool's reign of terror rough up Dare as a warning to the hit man, but this only serves to make him all the more bloodthirsty. Produced in part by Peter Lawford, Johnny Cool features an interesting variety of notables as Johnny's associates and victims, including Telly Savalas, Mort Sahl, Joey Bishop, Jim Backus, and Sammy Davis, Jr., who also sings the theme song.