Unnatural Born Killers

The day starts badly when a Cyberman is awoken halfway through its solar regeneration cycle by the needless Sontaran slaughter of an innocent people offering the hand of peace. Unable to start a war with the natives, the Sontarans begin genocide. The Cyberman, now fully recharged, defends the people and takes on the Sontaran force single-handed. Fighting his way aboard their colonisation ship, the Cyberman manages to destroy it, along with the bio-energy feed link with the surviving Sontaran ground troops. Returning to the people, he walks away, unable to share their joy. They remind him of so much that he has lost. He's called Kroton. He can't remember his real name.