Bit of an odd one this.

Half the audience will be overly excited at the prospect of Matt Smith’s Doctor dropping in on Sarah Jane and the gang, but there will also be a group that will be positively foaming at the mouth at the return of Jo Grant, a former companion of The Doctor, 37 years since she was last seen in Doctor Who (this reviewer was born during her final episode). Within moments, it’s like she’s never been away.

An absolute delight as Jo Grant, Katy Manning is everything that you’d hope she would be: charming, sweet, slightly ditzy, man-mad, and very funny at the same time as being very moving. Jo Grant (now Jo Jones, leading to another one of those ‘Smith and Jones’ gags) was very much the archetypal companion – even more so than Sarah Jane in many ways.

Jo was always unquestionably loyal when her immediate successor was more inclined to argue, and indeed it was with Jo that the phrase ‘what’s that, Doctor?’ gained much of its popularity.

The Sarah Jane Adventures proves once again that it’s something other than just a kids’ show, as the main themes explored within its relatively short running time are a lot smaller and personal – and a lot more important – than the world ending. As well as that, this is a total continuity fest, from tantalising references to Jo Grant’s immediate predecessor, to a mention of… well, we don’t want to spoil the surprise. Because, despite the title, this is very much a couple of episodes of ‘The Jo Grant Adventures’ – fast-paced, breathless, and, simply, fun.

You’ll note that we’re hardly mentioning Matt Smith’s appearance (you’ll have to wait to see if he’s actually dead or not), and that’s mainly because, aside from a not-at-all contentious line about how many lives he’s got left which can be ignored or taken as gospel as you see fit, these episodes aren’t really about The Doctor.

We haven’t had a chance to press pause that often, but we think there’s a fair chance that there’s a visual reference to pretty much every classic adventure featuring Jo and Sarah (don’t be too surprised if there’s a spike in DVD sales of Pertwee stories after this) and even the monsters look and sound like classic early ‘70s creatures (not a whiff of CGI here, thanks).

In short, while this is still a rollicking good two-parter for the kids, while for everyone else, this is so gleefully, joyously fan-boy it hurts, complete with lots of corridors to run down (‘Ventilation shafts! This takes me back!’).

There’s also that standard of Russell T Davies’ writing: massive plot points left dangling for any future writer to run and play with if they so wish. A highlight of the season – which it would be even if it turned up on its parent show.

Delightful.

Airs at 5.15pm on Monday 25th October 2010 and Tuesday 26th October 2010 on CBBC.