Following the death of his fiancee Peggy at the hands of heroin smugglers, Dr David Keel vows to track down the killers and avenge his lost love. He is aided in his quest by a mysterious stranger, John Steed.

Steed has infiltrated a gang, led by Mason, which is implicated in Peggy's murder. Steed asks Keel to establish contact with a rival gang, and the doctor discovers that Vance's hitman, Spicer, has been sent to kill Steed.

When representatives of the two organizations head to a country church to investigate the sudden reappearance of a man long thought dead, Steed and Emma are called in to help. It isn't long, of course, before murder rears its ugly head.