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.
| Writing | Robert Holmes | Writer |
| Production | Graham Williams | Producer |
| Directing | Norman Stewart | Director |
| Writing | Anthony Read | Script Editor |
| Sound | Dudley Simpson | Music |
| Production | John Nathan-Turner | Producer |
