It's really good all the way through, until at the end it gets even better. That was a genuinely emotional climax, which isn't to do with time-twiddling paradox theory (as you'd expect from the plot) but about a character making a painful choice. It's well acted, it's moving and it's clearly a high point for storytelling in the Doctor Who universe in general, not just for The Sarah Jane Adventures.

Firstly, it's the best work I've seen so far from Gareth Roberts. Does that include all his Doctor Who work as well? Yes, I think so. His name's on half of this show's first season, including Invasion of the Bane, but his first two stories struck me as perfectly competent bog-standard Who with some unlikeable characters. They were good TV. No more, no less. To be honest this one's even more of a genre trope, something we've all seen before with its roots in a gazillion classics: Dickens (A Christmas Carol), Capra (It's A Wonderful Life), Buffy the Vampire Slayer (The Wish) or Hitchcock (almost all of it). However it's still a strong concept that's scary, freaky and doesn't depend on rubber-suited monsters. It's certainly more powerful than simply killing people, which can get old even in regular movies and is likely to be doubly underwhelming in a children's show like this. It's not surprising that the Trickster not only became a regular villain in The Sarah Jane Adventures, but even got a promotion back into the parent show by proxy and killed the Doctor in Turn Left.

I hate parallel universes, but this isn't one. It's presented throughout as real and consequential and the story never goes into "ho-hum, this is all going to be unhappened again" wheel-spinning mode. I wouldn't always say that of Turn Left, for instance.

I like the resonances. I'm not saying they're necessarily deliberate, but I was reminded of both the Hellraiser and Phantasm horror franchises. The Trickster is practically another Cenobite, with his Faustian deals and his sinister puzzle box, while the Phantasm similarities involve enslaved dwarf-like aliens being used to kidnap Earthlings and take them to unearthly worlds on another plane of existence. Those interested me, but as a Doctor Who fan I should think I'm meant to be discussing the Black Guardian. Look at this Trickster. He's an agent of chaos who uses mortals as his pawns, talks about ephemerals and is going to come nearer than anyone in the universe before him to destroying the Doctor. "Waking or sleeping, I will be with you always..." This surely has to be deliberate, especially from an old fanboy like Gareth Roberts who'd even put the Black Guardian in one of his Doctor Who books, but having said that I don't think it's the guy himself. He seems more of a servant, like the Shadow from The Armageddon Factor. "I exist only to bring disorder. That is my purpose." He also says that chaos and blind chance are "food for me". Purpose? Food? That sounds to me more like a tool than the ultimate puppetmaster, which would have the incidental benefit of allowing either reading of his ambiguous line about "your memories of this Doctor". Had he already heard of the Doctor or not? Personally I thought he had, but we can take it either way.

Unfortunately the Trickster isn't the only alien in the show. There's also the comedy midget alien played by Jimmy Vee, who's a comedy midget alien played by Jimmy Vee. Why, it's the Graske, from that interactive Doctor Who mini-episode written by... would you believe it, Gareth Roberts! Of course as always he's very funny and Jimmy Vee should not only appear in every episode but also the title sequence, but I didn't think he belonged here. Ah well. The episode's strong enough to get away with it, just about, but it's still making the space pig in Aliens of London look like Laurence Olivier's Richard III.

While I'm on the subject of the acting, by the way... Ooooh, I love the cast in this one. There's Maria's Gay Dad! Not only does he have a lot of screen time (which is good in itself), but he's also been given a central story role and lots to do. Joseph Millson is cool. Note that he manages to stay likeable even when the plot needs him to be the pig-headed rationalist who won't listen to his daughter, but fortunately he later gets to be our hero too. This show should have been the Maria's Gay Dad Adventures. He also gets a few more homosexual undertones, one of which looks like as if it might have been thrown in by the actor rather than scripted. I'm talking here about his "eurghh" at the idea of women's football.

Great as he is though, even bit as good is Jane Asher. She's being given a surprisingly weighty role and she's doing a lot with it, both in giving full value to the emotional scenes and in the subtler stuff she's doing in between. Watch her carefully and you'll see a lot of layers in there, but the most important thing she does is to sell the finale. That was outstanding by proper dramatic standards and enough on its own to justify the existence of this entire show. The accent she's chosen surprised me, though. Obviously it also doesn't hurt that she's gorgeous. Spookily she's incomparably more attractive than the teenager who's playing herself forty years earlier, despite the fact that this girl looks quite a lot like Asher herself used to. (Ironically teen-Sladen is a better actress than teen-Asher.) Oh, and now that Jane Asher has taken the lead roles in "Whatever Happened to Susan Foreman?" and "Whatever Happened to Sarah Jane?", in future years I'm looking forward to seeing her take similar roles for other S-named Doctor Who companions like Steven Taylor, Sara Kingdom, Stacy and Ssard, Sam Jones and maybe even (if we're lucky) Sergeant Benton.

I should also mention the regulars. Yasmin Paige steps back into the limelight and does well, for instance managing to pull off an "and nothing is going to stop me" speech. That could have been nasty. Seriously, she's good. I was impressed. Meanwhile Tommy Knight and Daniel Anthony are improving the episode by getting sidelined, although to be fair Anthony does an efficient job in all the scenes he does get except "she did it". It helps that he's not being given supposedly cool dialogue, thank goodness, although inevitably he gets to look like a knob again with "too old for a skateboard".

Finally there's Sladen. Obviously she's nowhere near the league of a Jane Asher, but at her level she's still doing her usual solid work. I liked her too.

There are a bunch of details I liked too, e.g. the meteor. That's one of the neatest, slipperiest ways I've seen of quietly raising the stakes to "apocalyptic" without making a big deal of it. The 1950s was one of the fifties-est 1950s we've seen, although obviously the best stuff is all in the scene-setting shots. Fundamentally though, this story is seriously good. If you're interested in Doctor Who, there's no excuse for not watching it.