Doctor Who (season 20)

The twentieth season of British science fiction television series "Doctor Who" began on 3 January 1983 with the story "Arc of Infinity", and ended 16 March 1983 with "The King's Demons". A 20th Anniversary special, "The Five Doctors", followed in November 1983.
Casting.
Main cast.
Peter Davison continues his role as the Doctor, accompanied by Tegan Jovanka (Janet Fielding). While Nyssa (Sarah Sutton) leaves halfway through the season in "Terminus", Mark Strickson arrives as new companion Vislor Turlough in "Mawdryn Undead". In the penultimate serial of the season, the shape-shifting android Kamelion (voiced by Gerald Flood) is invited aboard the TARDIS after the Doctor frees him from the Master. Kamelion accepts, though the character itself would only be seen again in Season 21's antepenultimate serial, "Planet of Fire".
Past Doctors return for the 20th Anniversary special, with Patrick Troughton and Jon Pertwee appearing as the Second Doctor and Third Doctor. The First Doctor returns, played by Richard Hurndall as original actor William Hartnell died in 1975. Tom Baker was asked to return to play the Fourth Doctor but declined.
Past companions Elisabeth Sladen (Sarah Jane Smith), Nicholas Courtney (Brigadier Lethbridge-Stewart), Carole Ann Ford (Susan Foreman) return for the 20th Anniversary special, whilst Nicholas Courtney also makes an appearance in "Mawdryn Undead".
Recurring stars.
Anthony Ainley returns as the Master yet again in "The King's Demons" and "The Five Doctors".
The Black Guardian played by Valentine Dyall also makes a return in "Mawdryn Undead", "Terminus" and "Enlightenment".
The Castellan played by Paul Jerricho appears in "Arc of Infinity" and reprises the role in "The Five Doctors"
Guest stars.
Additional companions Frazer Hines (Jamie McCrimmon), Wendy Padbury (Zoe Heriot), Caroline John (Liz Shaw) and Richard Franklin (Mike Yates) make cameos throughout the special.
Returning villains for the season are Omega ("Arc of Infinity"), Cybermen ("The Five Doctors") and The Mara ("Snakedance"). A lone Dalek and a lone Yeti appear briefly in "The Five Doctors".
David Banks makes his second of four appearances in the show in "The Five Doctors" as a Cyber-leader.
Colin Baker, who was subsequently cast as the Sixth Doctor, made his first appearance in "Doctor Who" as Commander Maxil in the season's first serial, "Arc of Infinity", becoming the first actor to appear in the programme prior to taking on the role of the Doctor.
Serials.
To commemorate the twentieth season, the stories in this season involve the return of characters or villains seen in previous seasons. This season was broadcast twice weekly on Tuesday and Wednesday evenings on BBC1. It includes "The Black Guardian Trilogy", consisting of the serials "Mawdryn Undead", "Terminus" and "Enlightenment" and involving the arrival of Turlough, the departure of Nyssa and a single guest appearance from Brigadier Lethbridge-Stewart. Overall, these serials form a rough twelve-part epic.
Although "The Five Doctors" was broadcast more than eight months after Part 2 of "The King's Demons", which was the last regular story of the season, it is usually included as part of Season 20.
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Broadcast.
The entire season (including the show's 20th anniversary special "The Five Doctors") was broadcast from 3 January to 25 November. Transmission moved to Tuesdays and Wednesdays, except for the first episode of "Arc of Infinity".