The Doctor and Romana arrive on the marsh moon of Delta Magna in search of the next segment of the Key to Time. They are caught in the conflict between the native Swampies and the crew of a chemical refinery. The presence of a gun runner complicates matters; to make things worse, the Swampies intend to awaken Kroll, the giant god that lives beneath the swamps.
Unfortunately the movie Doctor Who: The Power of Kroll is not yet available on HBO Max.
| Directing | Norman Stewart | Director |
| Writing | Robert Holmes | Writer |
| Production | Graham Williams | Producer |
| Writing | Anthony Read | Script Editor |
| Production | John Nathan-Turner | Producer |
| Sound | Dudley Simpson | Music |
