Doctor Who - Season 20 (1983)

The High Council creates a distraction so the Doctor and Nyssa can find Omega on Earth and prevent his reentry into our universe.

The TARDIS lands on Manussa where Tegan once again gets possessed by the Mara, who plan to break into the physical world.

The Doctor talks to Ambril and Chela to try and stop the 500th anniversary celebrations. A possessed Tegan finds herself in Dugdale's Hall of Mirrors to where she summons Lon. The Doctor and Nyssa return to the caves.

The possessed Tegan and Lon try to find the whereabouts of the Great Crystal. The Doctor finds himself in prison, with only Nyssa to try and get him out. Chela tells the Doctor tales of Dojjen.

Escaping from jail and rescued from execution by Tanha, the Doctor escapes to find Dojjen. Will he finally be able to defeat the Mara?

With the TARDIS trapped on a collision course with a strange, orbiting spaceship, locked in time as well as space, the Black Guardian recruits a deceitful and ill-natured British student to kill the Doctor.

In 1983 the Doctor is once again reunited with his old friend Brigadier Lethbridge-Stewart, only the Brigadier struggles to remember his adventures with the Doctor. Meanwhile Tegan also meets the Brigadier in 1977.

While Nyssa, Tegan and the 1977 Brigadier debate whether or not Mawdryn is really the Doctor in a new body, the Doctor and the 1983 Brigadier explore the spaceship as the Black Guardian uses Turlough to awaken the rest of Mawdryn's people.

Mawdryn presents the Doctor with an ultimatum; give up his remaining regenerations or leave the ship and suffer the consequences. Meanwhile Turlough's stupidity puts the two Brigadiers at risk of meeting, angering the Black Guardian.

With the Black Guardian's guidance, Turlough begins sabotaging the Tardis which causes it to latch onto a seemingly empty passenger ship where the Doctor and Nyssa meet two space pirates and find themselves boarding space station Terminus.

The Doctor's party remains divided and scattered as the immense transport docks at the Terminus space station, which turns out to be a leper colony at the exact center of the known universe. As they find their way around and investigate, Nyssa shows signs of contracting the disease.

Since the Doctor's party represents neither lazars nor handlers, they're presumed to be investigators, which is enough to spark the disgruntled Valgard into challenging Eirak over leadership of the handlers. Meanwhile, as the giant, dog-like Garm takes a terrified Nyssa off for "treatment," Bor returns from the forbidden zone with interesting news about the ship.

In attempting to reopen a doorway into the TARDIS, Turlough activates Terminus' automated fuel-jettisoning sequence. The first time this sequence was engaged, it flung its first of two massive loads of unstable fuel into the distant past, producing the Big Bang that created the universe. This second sequence - if the Doctor can't find a way to shut it down - will release a second massive load, the explosion of which will entirely negate the effects of the first.

The Doctor is in a race with the clairvoyant Eternals for the prize. When the Black Guardian appears, though, the Doctor is suddenly in a race for his life!

Captain Striker and his officers reveal themselves to be Eternals, mind-reading creatures who live outside of time and who require Ephemerals (humans and other "time dwellers") to relieve them of their emptiness. They race against other Eternals for the grand prize of Enlightenment, by which to grant their deepest wishes. That can't be good for the universe, but how can the Doctor strategize against beings adept at reading his every thought?

Jumping overboard to escape the Black Guardian, Turlough lands on the Buccaneer, a pirate ship captained by the ruthless Captain Wrack who invites her rival Eternals aboard her ship to eliminate them from the race.

As the race nears it's end and the Black Guardian's victory seems all but certain, his counterpart, the White Guardian offers Turlough one final choice.

The Doctor, Tegan and Turlough arrive at an English castle in the year 1215 where King John welcomes the trio as demons. Noticing the King's strange behavior, the Doctor suspects he is actually an impostor.

With The Master revealed, two questions remain: Who is impersonating King John and why?

The Doctor and his previous incarnations are brought to the Death Zone on his homeworld Gallifrey as part of a renegade Time Lord's scheme.