When an experimental tidal power generator needs its eco-friendly credentials checked, Kate Stewart calls in an expert. Soon, Jo Jones is bound for ‘Project Charybdis’ in the South Atlantic, along with an awestruck Osgood. But out at sea, a treacherous plan is set in motion to awake an ancient race. Beneath the seabed an army is sleeping - an army of Sea Devils!
| Name | Type | Role | |
|---|---|---|---|
| Katy Manning | Guest Star | Jo Grant | |
| Ingrid Oliver | Guest Star | Osgood | |
| Nicholas Briggs | Actor | Sea Devils | |
| Jemma Redgrave | Actor | Kate Stewart |