Aimée Delamain

Whilst on a top secret security assignment, Tara comes under suspicion of being a double-agent. She must cast similar suspicion on Steed if she is to prove that she has been framed. An enemy agent, Gregor Zaroff, hopes to put the Government's new anti-missile defense system, code named 'Field Marshall', out of action by convincing Steed and Mother that Tara has betrayed the system's secrets.

Michael Dyter, the newly elected M.P. for South East Anglia, is assassinated after he has threatened to expose a government plot concerning the theft of a nuclear warhead. Mrs. Gale replaces him as a potential political candidate but she and Steed discover that Dyter is actually alive and in possession of the war-head, which he intends to set off on November the Fifth.