Space: 1999 2x19

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 unconscious in the Medical Center, Koenig is approached by one of the aliens (for that is what they really are) who tries to smother him...