Season 20

Season 20 of Doctor Who was Peter Davison's second season as the Fifth Doctor, and it ran between 3 January 1983 and 16 March 1983. Before the season ended, Nyssa had departed, Turlough had arrived, and the Brigadier had returned. Every story of this season contained an old enemy of the Doctor in at least a minor role, to celebrate the twentieth anniversary of the show.

Structurally, the season retread season 18's formula of including a trilogy of stories bound together by an overarching theme. In this instance, the tripartite tale involved Turlough's attempts to kill the Doctor at the behest of the Black Guardian.

Overview
Season 20 was notable for the degree to which it varied from its original plans. It had been commissioned as a 28-part series, and the intent was that it would have actually been broadcast towards the end of 1982. Producer John Nathan-Turner had hoped to use season 20 as a way to reverse the January-March broadast of season 19. Thus, he had initially obtained permission to record and broadcast season 20 in 1982, thus making season 21 broadcast over the milestone 23 November 1983. Had JNT got his way, the twentieth anniversary special would have in fact been a part of the regular twenty-first season.

Although this idea was in fact greenlit, permission had to be rescinded when it was discovered that Davison's second job — the then-popular BBC One comedy,   — wouldn't allow for this more aggressive Doctor Who production schedule. BBC One controller, Alan Hart, had to personally step in to settle the dispute between the two production teams, and he "awarded" Davison to Sink or Swim. This meant that season 20 would, like its predecssor, be broadcast in the first quarter of 1983.

Hart, however, did want some sort of anniversary special in November, so he suggested that JNT put the money for two of the 28 episodes aside to allow for the special. This of course meant that there would now be 26 episodes in season 20. In the end, however, the final four episodes — meant to go towards a Dalek adventure that eventually became season 21's Resurrection of the Daleks — were left on the table because of a union dispute. Thus, as transmitted, season 20 consisted of just 22 episodes.

Meanwhile, the anniversary special, which was originally envisaged as a part of season 21, was something quite separate from any season. Although it used a portion of the original money involved in the season 20 commission, it received a separate commission from Head of Series David Reid on 15 July 1982, long after season 20 had wrapped. Indeed, it only received this commission because JNT had been able to secure co-production money from the main Australian network. Moreover, The Five Doctors, as the production was eventually called, didn't begin principal photography until early March 1983 — just when season 20 was wrapping transmission on television.

The Five Doctors, though often said to be a part of season 20, was therefore not a part of season 20 in any production or broadcast sense. Indeed, it's doubtful that any contemporary viewer thought of it as a part of the season, since it came almost eight months after the closing scene of The King's Demons. Instead, it had much greater production and broadcast proximity to season 21.

Regulars

 * The Fifth Doctor - Peter Davison
 * Tegan Jovanka - Janet Fielding
 * Nyssa - Sarah Sutton
 * Turlough - Mark Strickson

Semi-regulars

 * The Black Guardian - Valentine Dyall

Stories set during this season

 * BFA: Omega (immediately after Arc of Infinity)
 * PDA: Fear (between Arc of Infinity and Snakedance)
 * PDA: Zeta Major (between Arc of Infinity and Snakedance)
 * MA: The Sands of Time (between Arc of Infinity and Snakedance)
 * MA: Goth Opera (between Snakedance and Mawdryn Undead)
 * BFA: Cobwebs (between Terminus and The King's Demons)
 * BFA: The Whispering Forest (between Terminus and The King's Demons)
 * BFA: The Cradle of the Snake (between Terminus and The King's Demons)
 * MA: The Crystal Bucephalus (between The King's Demons and The Five Doctors)

VHS

 * Arc of Infinity
 * Snakedance
 * Mawdryn Undead
 * Terminus
 * Enlightenment
 * The King's Demons/The Five Doctors (extended version)

DVD

 * Arc of Infinity (2007)
 * Snakedance (2011)
 * The Black Guardian Trilogy (contains Mawdryn Undead, Terminus & Enlightenment) (2009)
 * The King's Demons (2010)

Novels

 * Arc of Infinity
 * Snakedance
 * Mawdryn Undead
 * Terminus
 * Enlightenment
 * The King's Demons