The Magellanic Clouds, the planet Ribos, an unknown time. Ordered by the White Guardian to collect the pieces of the omnipotent Key to Time, The Doctor, K-9 and his new assistant Romana arrive. Collecting the first segment is not going to be easy…
| Name | Type | Role | |
|---|---|---|---|
| Robert Holmes | Writer | ||
| Oliver Maguire | Guest Star | ||
| Nigel Plaskitt | Guest Star | ||
| Robert Keegan | Guest Star | ||
| Iain Cuthbertson | Guest Star | ||
| Paul Seed | Guest Star | ||
| Cyril Luckham | Guest Star | ||
| John Harmill | Guest Star | ||
| George Spenton-Foster | Director |