When the inhabitants of Delta Magna, the Swampies, were relocated to the third moon of their planet, they carried with them many legends and holy relics. One of these legends concerns a squid-like beast, known as Kroll, seen by the Swampies as their God. Many years later, a giant squid-assumed to be Kroll-swallowed one o the Swampy Holy Men along with a Holy Relic and was never seen again. When the colonists then turned their attention to the third moon, placing on experimental methane refinery in the swamp area, the Swampies again realized that their lifestyle was being disrupted. They prayed that Kroll would once more rise to strike their enemies down. This Kroll apparently did, now grown to roughly a mile in diameter, complete with countless tentacles; Kroll however was incapable of discerning between humans and Swampies, satisfying its hunger with either. The Doctor realized that the Holy Relic it had swallowed was the fifth segment to the Key to Time and its metamorphic properties had increased Kroll's size over the centuries. He was unable to use the Tracer against Kroll, retrieving the segment and killing Kroll by separating it into lots of tiny dead squids.