The Bringers of Wonder: Part 2 (S02E19)

People from Earth have landed on Moonbase Alpha, promising to take the Alphans back home. Commander Koenig, however, sees not fellow human beings, but aliens, and tries to kill some of them. Horrified, Helena stuns him with a laser gun and later, as he lies unconcious in the Medical Centre, Koenig is approached by one of the aliens (for that is what they really are) who tries to smother him. (iTunes)