A notorious killer, long believed to have died in Australia, returns to England seeking revenge for the death of his sister. The "Ringer" threatens to murder the criminal mastermind Maurice Meister. Detective Inspector Alan Wembury is assigned to the case and, despite his strong dislike for Meister, attempts to protect him with the reluctant assistance of another criminal, Sam Hackett, who has been released from prison as he is the only man able to identify the "Ringer". Even with his help, Wembury struggles to unmask their target before the time at which Meister is due to be killed.
