While Ara tries to save Polly from being turned into a Fish Person and Ben and Jamie try to escape from the mines, the Doctor discovers the full extent of Zaroff's plans.
Did You Know?
This episode was wiped by the BBC and no copy of it was known to exist, until December 2011 when it was recovered from a former ITV engineer. See more
[close-ups of hypodermic being filled from a bottle
One tiny jab, and you'll know nothing more about it until it's all over.