The Sontaran Experiment


The Doctor agrees to transmat down to Earth to make sure everything is okay before the Nerva survivors begin to reclaim their planet.

There, he, Sarah Jane and Harry discover the presence of a Sontaran named Styre, who is performing cruel experiments on a band of captive humans.

Styre's goal is to discover the weaknesses of the human body -- weaknesses the Sontarans will then exploit in their quest to dominate the universe.