Sarah is the first companion to get neither a joining scene nor a first look inside the TARDIS (even Dodo, Ben and Polly got those). Uniquely, her companionship is a fait accompli, and rather than being sent back with Rubeish and the other research scientists she leaves with the Doctor. Having spent the first half of the story suspecting he’s somehow responsible for the kidnaps, this is a pretty comprehensive volte face. It’s sets Sarah up as being a bit different from previous companions – Jo’s official job was being the Doctor’s assistant, whereas Sarah has an independent career back on Earth that she’ll occasionally return to. In this, she’s more like a new series companion, always with one foot outside the TARDIS, UNIT and the Doctor’s world.

Elisabeth Sladen is instantly impressive, and gets loads to do throughout the serial including, in this episode, disguising herself as a serving wench and trying to incite a below-stairs feminist revolution, encouraging the kitchen women to ‘tell the men you’re tired of working for them like slaves’ (‘We are slaves,’ Meg replies wearily). Then she rescues the Doctor (again) from death before Irongron’s incompetent firing squad, and sends Rubeish back to the 20th Century. And she apparently enjoys every moment of it.

The Doctor equally seems to be enjoying himself, making quips as he dodges bullets, swinging on a chandelier like Errol Flynn, and dressing up as a robot for some very flimsy reason (still, it leads to the funniest line of the episode as Irongron plans to dismember the robot to test how dangerous it really is, prompting the Doctor to ask, ‘Isn’t that a bit unsporting, old man? I mean, sitting ducks and all that.’) Through the story he’s been set up as a counterpart to Linx. The point that Linx is trapped on one planet and forced to work as a kind of scientific advisor to the local military has been made many times before. Here, the comparisons are explicit, as the Doctor impersonates Linx himself, and makes it clear that he, unlike the Sontarans, is very concerned about the fate of the “primitives” Linx disdains – to the extent that even now he’s got his freedom back he’ll keep helping the Brigadier and UNIT.

Given how much it does – introduce Sarah Jane, the Sontarans and the most enduring version of the title sequence; reintroduce historical stories; mark the 10th anniversary much more closely than The Three Doctors – The Time Warrior is slightly neglected. This is mystifying. Aside from the direction, which is unspectacular (and falls apart a bit in the climax, which lacks the drama and crispness of something like The Dæmons), it’s exceptionally good. Robert Holmes’ script is his best yet, more than justifying the imminent decision to make him Terrance Dicks’ successor as script editor. Pertwee and Sladen are an instantly winning combination (no mean feat after three years of Katy Manning). The Sontarans are brilliant inventions, brilliantly realised. And given this was, like Carnival of Monsters, made at the tail end of the 10th season and held over to open the 11th, it shows no signs of the cast or crew flagging. This is one of the best stories of the 1970s.

Next episode: Invasion of the Dinosaurs