Fourth Doctor and Sarah Jane Smith adventure from 1975.

The story opens with the time travellers arriving in a beautiful leafy English Wood, but The Doctor senses that something is out of place. When the pair witness a UNIT soldier walking to his death over a cliff they decide to investigate, and uncover an alien conspiracy to gradually replace the Earth with android replicas of humans and infiltrate before taking over.

Starring  Tom Baker as the 4th Doctor.

DVD is in very good but used condition.