Borb, the president of the Balkan Republic, is visiting London to sign a military deal. His private secretary is killed by a masked wrestler, the Decapod. Steed is assigned to augment the president's bodyguards, but the wrestler continues to kill those close to Borb.

Steed is trying to infiltrate a group of assassins currently based in the South of France. He robs the leader of some jewellery in order to impress him, then waits for them in the local club. It just so happens that Venus Smith is singing there.

Classified information is finding its way into the wrong hands and Steed feels sure that this has something to do with the death of the magician's assistant at the club where Venus Smith is working. Steed investigates the lethal vanishing cabinet.

Steed, investigating the suicide of a University tutor, discovers that the man seems to have shot himself with a gun with a silencer attached. Venus is sent a tub of acid 'face-cream', and there is another mysterious suicide.

Venus has her camera and films stolen whilst taking pictures in a fun fair. One film is missed, however, and when developed a face can be seen in the Hall of Mirrors - that of Trevelyan, the cypher clerk who has committed suicide. But Venus's photograph was taken after the man's death.

A holiday for Steed in Greece is, of course, no straightforward affair. A deep-sea diver dies in mysterious circumstances, whilst bathyscope experiments are taking place on the yacht where Venus is singing.