Parts: 4
Writer: Robert Holmes
Airdates: 23 December 1978 - 13 January 1979
Production Code: 5E

Doctor: fourth
Companion: the first Romana, K-9 mark two

Creature Feature: Kroll

Story: K-9 is marooned in the TARDIS when it lands on the swampy third moon of Delta Magna. Romana finds that the fifth segment's signal is diffused over a wide area, and when she moves to higher ground to get a better reading, she is kidnapped by the Swampies, the green-skinned natives of Delta Magna III. The Doctor, meanwhile, is shot down by the crew of a nearby methane refinery, who mistake him for the gun-runner Rohm-Dutt.

The refinery crew are on edge because the Swampies have been acting more rebellious of late, and they fear that sympathizers on Delta Magna may be aiding them in planning an attack on the refinery. To add to their troubles, the surface of the lake bed keeps shifting, worrying them that the rich source of methane may be disturbed. The Doctor's appearance is not well-received. Meanwhile, in preparing for their upcoming battle against the refinery that threatens to take over their latest home, the Swampies have decided to present a sacrifice to their protector, Kroll...and Romana has been cast in the lead role.

While the Doctor manages to free Romana and escape, soon they have both been recaptured by a group of angry Swampies. Assuming that the Doctor and Romana can escape the slowest of the Seven Holy Ritual executions, they have much bigger problems to worry about. Literally. At the bottom of the lake, something is stirring - and it just happens to be very hungry, very bad-tempered and very large...