The striking new title sequence and logo emphasise that this is a new beginning of sorts for the series. With the UNIT Fam broken up, the Doctor free to roam time and space, and (behind the scenes) Barry Letts and Terrance Dicks looking to move on, the transition to the Tom Baker years is beginning. Which makes this something like The Invasion in Season Six: a story that features the current team, but anticipates many of the elements of the next era of the show. In this case, most notably the arrival of Sarah Jane Smith, a character that will go on to surpass Jo Grant both in tenure and popularity.

It’s a very different introduction than Katy Manning got. Jo was instantly set up as a ditzy partner for the Doctor. Sarah Jane is more of a foil for him, initially coming across as fairly abrasive and confrontational where Jo tended to be conciliatory and charming. While it’s easy to get these kind of relationships wrong (as several 1980s episodes do), it works here, though. Partly because Robert Holmes’ script emphasises the screwball comic potential of the relationship (the Doctor teasing Sarah about making coffee, and his “alarm clock”), and partly because Pertwee and Elisabeth Sladen have an immediate rapport, with Pertwee positively sparkling as he faces someone with a bit of spark rather than another dull middle aged scientist or soldier. We don’t see much of what Sladen will bring to the role, but the way she’s established, as an independent character who’ll snoop undercover, stow away in the TARDIS, and kick and berate when she’s abducted by a medieval ruffian are a novel contrast to Jo’s style.

There’s novelty, too, in the setting. We haven’t been to a recognisable bit of Earth’s history for four years. Like The War Games, this opens in the past, and then starts to throw in anachronisms – an alien spaceship arriving in the middle of an Errol Flynn movie is startling, even if it’s just a twist on The Time Monster‘s historical characters visiting the present. Having events in another time zone affect the present, with Linx appearing as a ghost in armour, also recalls Day of the Daleks, so this starts to feel like Holmes and Dicks picking bits out of older stories in a way that in less skilled hands could look like they’re running out of ideas, but instead comes across as variations on a theme. 

It helps that Linx the Sontaran is a masterful creation: well-spoken (it almost sounds like Kevin Lindsay is doing a Pertwee impression), intelligent and as annoyed at being trapped with a bunch of primitives as the Doctor was back in Season Eight. His little speech as he claims Earth for the Sontaran Empire, his enjoyment at the idea of battle, and the excellent costume and mask design add up to an immediately classic monster, probably only second to the Daleks in getting it right first time. Apart from The Five Doctors, this is the first Pertwee story I saw when I got the movie-edit VHS, so the cliffhangers still come as a bit of a surprise. This one is brilliant: a turn into a camera zoom to reveal that potato face, tongue flicking over the lips, intelligent eyes scanning the courtyard. Marvellous.

Next episode: The Time Warrior – Part Two