The huge, octopus-like Kroll lived deep in the swamps of the humid, steamy planet.
To the native swamp-warriors, Kroll was an angry, mythical god. To the money-grabbing alien technicians, Kroll was a threat to a profit-making scheme.
In their search for another segment of the Key to Time, the Doctor and Romana have to face the suspicion of the Lagoon dwellers, the stupidity of the technicians and, finally, the power of Kroll...