Seabase 4 is on alert as a strange craft approaches. But the crew has been infiltrated by the enemy, so Commander Vorshak's solutions are scuppered at every turn.
| Name | Type | Role | |
|---|---|---|---|
| Johnny Byrne | Writer | ||
| Tara Ward | Guest Star | ||
| James Coombes | Guest Star | ||
| Norman Comer | Guest Star | ||
| Tom Adams | Guest Star | ||
| Nitza Saul | Guest Star | ||
| Nigel Humphreys | Guest Star | ||
| Vincent Brimble | Guest Star | ||
| Martin Neil | Guest Star | ||
| Ian McCulloch | Guest Star | ||
| Christopher Farries | Guest Star | ||
| Pennant Roberts | Director |