All four classic Doctor Who stories featuring the alien species, the Sontarans, who first appeared in the 1973 story, 'The Time Warrior'. The Sontarans are a self -cloning race who live in a militaristic society in the 'southern spiral arm of the galaxy'. Humanoid in appearance, with a squat build and distinctive dome-shaped heads, they are far stronger than mere humans and possess an unquenchable thirst for war. The other stories in this set are 'The Invasion of Time' (1977), 'The Two Doctors' (1984) and 'The Sontaran Experiment' (1975).