At Marseilles airport, Steed and Cathy find the courier they were due to meet dead. His sample of new liquid rocket fuel has been taken. Facing an array of enemy agents, the duo must recover the flask of Propellant 23.

When Sir Gerald Bancroft and his Rolls-Royce vanish whilst being escorted at a military base, Steed is called upon to solve the puzzle. But before he can he experiences that old shrinking feeling.