Whilst travelling on an express train on a quest to find a missing agent, Steed and Mrs. Peel get caught up in an assassination attempt on the life of the British Prime Minister on the part of a disgruntled and murderous ticket collector. They are helped in their efforts to foil him by Mr. Crewe, an eccentric owner of an abandoned station.

Reliable men are reverting to childhood, and blabbing all of their secrets to kindly old "Nanny Roberts."

Mrs. Peel is invited to a bridge party at a house on Exmoor but when she arrives she discovers that she has been lured there by a man known as 'The joker'. She had once helped to put him in prison, but he has now escaped and with his two crazy accomplices, subjects Mrs. Peel to a series of lethal tricks and traps as Steed arrives to help her.