Thomasine Heiner

UNIT are summoned to Wenley Moor research station which is experiencing mysterious power losses. In the nearby caves, one of the staff has been killed and another sent insane.

Investigating the caves, the Doctor is attacked by a dinosaur-like creature. Dr Quinn is hiding a secret that could endanger the lives of everyone.

The creature from the caves, wounded and dangerous, is on the loose on Wenley Moor. Dr Quinn attempts to recover it and is unwilling to listen to the Doctor's warnings.

When the Silurian leader is killed, all hopes of peace are lost. The Silurian's infect Major Baker with a virus deadly to humans and release him to spread the infection.