The Doctor is captured by the Sea Devils and taken to their undersea base. There he tries to make peace with the creatures, but his efforts are thwarted by the Navy.
| Name | Type | Role | |
|---|---|---|---|
| Malcolm Hulke | Writer | ||
| Martin Boddey | Guest Star | ||
| Rex Rowland | Guest Star | ||
| Colin Bell | Guest Star | ||
| David Griffin | Guest Star | ||
| Christopher Wray | Guest Star | ||
| Norman Atkyns | Guest Star | ||
| Michael E. Briant | Director |