The Doctor and Sarah Jane return to England after their Antarctic ordeal and Chase tries to eliminate them, but they escape and track him down at his estate, where he is preparing to open the Krynoid pod.

The Doctor is captured by Chase, who plans to breed the stolen Krynoid pod. He is placed in an automated compost hopper and only Sarah Jane can save him... but will she make it before the Krynoid grows to fruition ?

The Krynoid grows to a monstrous size and traps the Doctor and the others in a cottage. The creature demands they turn over the Doctor, while Chase seeks to make an alliance with the alien vegetation.