Jon Pertwee makes his final appearance as the series lead in Planet of the Spiders, although he would reprise the role of the Third Doctor in the 20th anniversary special episode, "The Five Doctors". Elisabeth Sladen makes her first appearance as Sarah Jane Smith in The Time Warrior.
Tom Baker makes his first uncredited appearance as the Fourth Doctor in Part 6 of Planet of the Spiders, when Jon Pertwee's Doctor is fatally wounded and regenerates into the Fourth Doctor.
This season was the last to have Barry Letts as producer and Terrance Dicks as script editor, ending the relationship that had gone through the whole of Jon Pertwee's tenure as the Doctor. It saw the introduction of a new logo that would be used nearly throughout the fourth Doctor's era, as well as the new companion Sarah Jane Smith and the alien race, the Sontarans.
In the Middle Ages, a rabble of criminals find the crashed spaceship of a Sontaran warrior. Meanwhile, in the 1970s, the Third Doctor is investigating the disappearance of several scientists from a top secret research complex.
A giant spider from the planet Metebelis Three is summoned to an English meditation retreat by an out-of-work salesman.
Broadcast
Episode one of The Time Warrior saw the first appearance of the iconic diamond-shaped Doctor Who logo. This would be used throughout the Third Doctor's final season and almost through the Fourth Doctor's tenure before retiring in part four of The Horns of Nimon (not including the unbroadcast and incomplete serial Shada which would have followed The Horns of Nimon).
The entire season was broadcast from 15 December 1973 to 8 June 1974.