The planet Solos in the 30th century. As Earth slowly moves towards granting Solos its independence, the Doctor and Jo arrive on a mission for the Time Lords. How far will the brutal Marshal go to retain his power over the planet? And why are the native Solosians undergoing a gradual mutation into hideous, insect-like creatures?
Elenco: William Hartnell , Patrick Troughton , Jon Pertwee , Tom Baker , Peter Davison , Colin Baker , Sylvester McCoy .