A number of businessmen have been mysteriously murdered, and their affairs taken over by their secretaries. The secretaries are part of a group of young professional women whose plan is to take woman out of the secretary's chair and put them in charge of the business. Their motto is “Ruination to all men".
Their plan is uncovered by Steed and Mrs Peel. In order to catch the gang, Steeds decides to hire one of the secretaries and Mrs Peel trains as a secretary in order to infiltrate the gang. Steed discovers that the secretaries use a filing system that is so complex, that they are the only ones capable of operating it, so when they murder the businessman they can easily take over.
Emma discovers that the secretaries meeting place is a keep fit gym, so she decides to enlist in the group. She manages to convince them that she is willing to join the gang and ready to murder her boss. However, he cover is blown by one of the secretaries who recognizes who she really is.
Steed discovers that the secretary he hired has been tasked with killing him. Before she can succeed he disarms her and then tickles her to make her reveal what the gangs motives are. He rushes to the gym in order to rescue Mrs Peel. A fight ensues, and Mrs Peel ends up fighting the whole group of leotard clad secretaries. She deposits them one-by-one on the floor, all unconscious.