On the planet Xeros, the TARDIS crew discover their own future selves frozen in time as exhibits in a galactic museum and must avert this potential future.
| Actor | Role |
|---|---|
 William HartnellThe Doctor | The Doctor |
 Jacqueline HillBarbara Wright | Barbara Wright |
 William RussellIan Chesterton | Ian Chesterton |
 Maureen O'BrienVicki | Vicki |
| PPeter SandersSita | Sita |
| PPeter CrazeDako | Dako |
| BBill StarkeyThird Xeron / Xeron | Third Xeron / Xeron |
| RRichard ShawLobos | Lobos |
 Jeremy BullochTor | Tor |
| SSalvin StewartMorok Messenger / Morok Guard | Morok Messenger / Morok Guard |
 Peter DiamondMorok Technician / Morok Guard | Morok Technician / Morok Guard |
| LLawrence DeanMorok Guard | Morok Guard |
| KKen NorrisMorok Guard | Morok Guard |
 Ivor SalterMorok Commander | Morok Commander |
| MMichael GordonXeron | Xeron |
| EEdward GranvilleXeron | Xeron |
| DDavid WolliscroftXeron | Xeron |
| BBilly CorneliusMorok Guard | Morok Guard |
 Peter HawkinsDalek (voice) | Dalek (voice) |
| MMurphy GrumbarDalek | Dalek |