‘You just want to mate?’ The annus mirabilis begins with a story reuniting the Doctor and Donna, a partnership so successful it’s being resurrected for Bad Wolf’s new series. Even at the time, this felt like a good move: Catherine Tate was an established TV star (whereas Rose felt more like a breakthrough role for Billie Piper, better known for other things) with broad appeal and – importantly – an excellent onscreen rapport with Tennant.

To make this work, Donna 1.0 from The Runaway Bride is repurposed into Donna 2.0, some of the spikiness and self-centredness smoothed down, and a lot of her more aggressive characteristics passing across to her mother. The show gets away with this because The Runaway Bride was 16 months ago, and some of Donna’s shriller aspects there can plausibly be accounted for by the fact she’d been abducted from her own wedding. Equally, RTD’s script suggests her day with the Doctor has had a lasting impact, making her pay more attention to the world and the people around her: she’s been changed for the better. This is fantastic sleight of hand, with a couple of headline moments (like ‘You just want to mate?’) that are pure Donna 1.0.

The other fantastic thing about this is the way it lightly but clearly places itself as part of a continuing story. The Doctor talks about his own feelings and behaviour towards Martha, and confirms that Rose is still lost (which also works as set-up for the brilliant end of episode surprise), Donna mentions the death of the Racnoss children, Wilf (hurrah, Bernard Cribbins) connects this back to the previous Christmas special, and – more subtly – when the Doctor is using two sonic devices against Ms Foster, Donna stops him from pushing it too far, living up to her observation that sometimes he needs someone to stop him.

The deftness of the character work and comedy hides the daftness of much of the plot, which has a cleverly topical idea (weight loss pills) but plays out as a battle between sonic magic wands and a big button in a cupboard. It moves with such fleetness, the dialogue is so enjoyable, the set piece scenes so charming that it’s barely noticeable that it’s about as substantial as a post-parthenogenesis Stacy. James Strong’s direction is perfectly pitched, emphasising the Doctor and Donna’s near-misses (including an opening sequence of them apparently walking towards each other in a crowded street that evokes the start of Smith and Jones), and the Doctor’s current lonely life as he talks to himself in a TARDIS that’s made to look bigger and emptier than ever. The result is one of the show’s finest screwball comedies, a brilliant set-up for the series ahead.

Next Time: The Fires of Pompeii