The Doctor has regenerated and all is not well. Confused, angry and acting strangely, the new Doctor decides to become a hermit, so takes his concerned companion Peri to a desolate asteroid where he plans to live for several centuries. However, the time travellers soon uncover a plot that threatens the entire galaxy. Why has an alien Gastropod kidnapped a pair of genius twins, and will the Doctor recover in time to find out?
| Actor | Role |
|---|---|
 Colin BakerThe Doctor | The Doctor |
 Nicola BryantPeri Brown | Peri Brown |
 Maurice DenhamEdgeworth | Edgeworth |
 Edwin RichfieldMestor | Mestor |
 Kevin McNallyHugo Lang | Hugo Lang |
| DDennis ChinnerySylvest | Sylvest |
| GGavin ConradRomulus | Romulus |
| AAndrew ConradRemus | Remus |
| SSeymour GreenChamberlain | Chamberlain |
 Oliver SmithDrak | Drak |
 Barry StantonNoma | Noma |
| DDione InmanElena | Elena |
| HHelen BlatchFabian | Fabian |
| RRoger NottPrisoner | Prisoner |
| JJohn WilsonJacondan Guard | Jacondan Guard |
 Graham ColeJacondan | Jacondan |