England, the near future. UNIT is providing security and scientific support for the Stahlman project, an attempt to tap the Earth's core for energy. But things are already going wrong…
| Name | Type | Role | |
|---|---|---|---|
| Don Houghton | Writer | ||
| Christopher Benjamin | Guest Star | ||
| Nicholas Courtney | Guest Star | ||
| Sheila Dunne | Guest Star | ||
| Derek Newark | Guest Star | ||
| Derek Ware | Guest Star | ||
| John Levene | Guest Star | ||
| Walter Randall | Guest Star | ||
| Ian Fairbairn | Guest Star | ||
| Olaf Pooley | Guest Star | ||
| David Simeon | Guest Star | ||
| Douglas Camfield | Director |