Doctor Who: The Sontaran Experiment (1975) (DVD)

The Doctor, Sarah and Harry arrive on a desolate and apparently deserted Earth to discover that a group of shipwrecked astronauts from a human colony, GalSec, have been lured there by a fake distress call. One of their number, Roth, tells Sarah of an alien conducting gruesome experiments on him and his crewmates. The alien turns out to be a Sontaran, Field-Major Styre, who is compiling a report on human physical and mental capabilities as a prelude to an invasion of Earth!

Audio Commentary with Elisabeth Sladen, Bob Baker and Philip Hinchcliffe
Documentary - Built for War. A brief history of the Sontaran race, told by some of the actors and production personnel who worked on the stories, including Elisabeth Sladen, stuntman Stuart Fell, writer Bob Baker and more
Photo gallery
Production notes