The Director of Operations (Disco) of the Nutshell, a subterranean World War III bunker, tells Steed and Cathy that Big Ben, a file giving details of all their double agents, has been copied. Security cameras point to a young girl, but she is later found dead. Evidence implicates Steed, and Disco orders that he be apprehended.

A government official, dresssed as one of the Horse-guards, helps in a raid on secret files and is wounded. Recovering, he remembers nothing. Is his crime anything to do with his membership of Ransack, a club for those with high IQs? Emma can join, but Steed may have to cheat....

When one of the Floral Network of agents is found dead atop a pair of stilts, Steed and Emma's interest is piqued. That's the idea, because foreign agents Basil and Lola have a trap prepared for them: a machine that swaps their minds into the pair's bodies.