Omega, an ancient Time Lord made of pure anti-matter, once defeated by the Doctor, is plotting to cross over into this dimension by bonding with the Doctor. Meanwhile, the disappearance of a man in Amsterdam piques the curiosity of his cousin, Tegan, who previously left the Doctor at Heathrow Airport and now finds herself at Omega's mercy. Fearing total destruction from the collision of matter and antimatter, the Time Lords recall the Doctor to Gallifrey to undertake the only viable solution: executing him!
| Actor | Role |
|---|---|
 Peter DavisonThe Doctor | The Doctor |
 Sarah SuttonNyssa | Nyssa |
 Janet FieldingTegan Jovanka | Tegan Jovanka |
 Leonard SachsPresident Borusa | President Borusa |
 Elspet GrayChancellor Thalia | Chancellor Thalia |
 Michael GoughCouncillor Hedin | Councillor Hedin |
| PPaul JerrichoThe Castellan | The Castellan |
| MMax HarveyCardinal Zorac | Cardinal Zorac |
 Colin BakerCommander Maxil | Commander Maxil |
| IIan CollierOmega/The Renegade | Omega/The Renegade |
| NNeil DaglishDamon | Damon |
 John D. CollinsTalor | Talor |
 Alastair G. CummingColin Frazer (as Alastair Cumming) | Colin Frazer (as Alastair Cumming) |
| AAndrew BoxerRobin Stuart | Robin Stuart |
| MMaya WoolfeHostel Receptionist | Hostel Receptionist |
| GGuy GroenHostel Receptionist | Hostel Receptionist |
| MMalcolm HarveyThe Ergon | The Ergon |