Genocide
Paul Leonard
 Jo Grant, a UNIT veteran, receives a call for help from an old colleague. A scientific unit is being threatened by a UNIT force led by a secretive Captain. Jo Grant ends up sucked out of time and space. Meanwhile, the Doctor and Sam go to 2109 and find an alien race where the humans should be. To make it worse, the aliens claim to have been there for thousands of years...and something is wrong with Sam's mind.