Ian and Vrestin fall into caverns beneath the surface of Vortis and encounter the Optera. The Doctor finds the landing site of the Menoptra, and the Zarbi prepare to ambush them.
| Name | Type | Role | |
|---|---|---|---|
| Bill Strutton | Writer | ||
| Jocelyn Birdsall | Guest Star | ||
| Ian Thompson | Guest Star | ||
| Barbara Joss | Guest Star | ||
| Arne Gordon | Guest Star | ||
| Catherine Fleming | Guest Star | ||
| Jolyon Booth | Guest Star | ||
| Richard Martin | Director |