When a colleague is found dead in a large London department store Steed and Mrs. Peel go undercover as staff members, exposing a dastardly plot by the wheelchair-bound Horatio Kane to devastate the capital with a huge bomb housed within the store.

When an agent in diving gear is found dead in a Scottish loch yet substantially taller than he was whilst he was alive Steed and Mrs. Peel visit a remote castle owned by the feuding De'ath cousins, Ian and Angus, to investigate the sinister goings-on.

Government minister Sir Clive Todd is wounded as he and other ministers try to steal top secret documents. He has no idea why he did it and hypnosis is suggested. All concerned belonged to a club for people with high I.Q.s called RANSACK, who are about to meet at a school. The Avengers join the club in order to expose the mastermind behind the next heist - the theft of a plane from an R.A.F. base.