An espionage ring is stealing secrets from the Government's top secret Cypher HQ, by posing as window cleaners.
Templar and the niece (Annette Andre) of a research scientist search through a labyrinth of tunnels underneath a mountain in Wales.
Steed and Cathy Gale find the worlds rarest stamp is the key to an evil and fantastic plot.
Steed hunts an informer only to find that he himself is suspect no. 1!
Steed faces the firing squad, Cathy becomes Pretender to the Throne.
