The Doctor meets Colonel Lethbridge-Stewart who takes control of the military operation against the Yeti. But the Doctor suspects that there is a traitor in their midst.
| Name | Type | Role | |
|---|---|---|---|
| Mervyn Haisman, Henry Lincoln | Writer | ||
| Jon Rollason | Guest Star | ||
| Jeremy King | Guest Star | ||
| Stephen Whittaker | Guest Star | ||
| Rod Beacham | Guest Star | ||
| Douglas Camfield | Director |