Strange diseases are being reported in various parts of the world, and Steed's suspicion is that somebody has been tampering with the insecticides and fertilisers of United Foods and Dressings. Cathy Gale is captured whilst investigating, and will be the 'guinea pig' for a test on the new strain of bubonic plague.
Elenco: Patrick Macnee , Honor Blackman , Diana Rigg , Linda Thorson , Ian Hendry .