The Doctor and Romana's investigation of the Hydrax's horrific operations and their escape from the ruling class

Having uncovered the Hydrax’s true nature, the Doctor and Romana ascend a long ladder to reach the turret of the great ship. There they find an intact Arrow-class scout ship, …

The Doctor and Romana descend into the restricted lower levels of the Hydrax where archaic fuel tanks hum with unseen processes. Romana's practical observation about their location is cut short …