The Doctor attempts to persuade Captain Hart of the danger that the Master represents. Eager to make contact with the Sea Devils, the Doctor journeys deep into the ocean.
| Name | Type | Role | |
|---|---|---|---|
| Malcolm Hulke | Writer | ||
| Colin Bell | Guest Star | ||
| David Griffin | Guest Star | ||
| Clive Morton | Guest Star | ||
| Stanley McGeagh | Guest Star | ||
| Brian Vaughan | Guest Star | ||
| Michael E. Briant | Director |