A Wedding. A nice big church, the wedding march plays and the bride walks up the aisle until a golden light surrounds her and she vanishes in a cloud of glowing dust that rises to the ceiling and passes through. The TARDIS is spinning through space and the bride materialises inside. Both she and the Doctor are very confused.

She’s very hostile. She thinks this is all some trick cooked up by her nemesis, Neris. Unfortunately the Doctor has no idea how she got there. She runs to the doors and opens them and is finally silenced by the view of the nebula outside. Her name is Donna.

The Doctor takes Donna back to Earth but the TARDIS isn’t well and they don’t arrive exactly where she wanted. While the Doctor fusses and natters on Donna steps outside and discovers the old, smaller on the outside business and walks off. The Doctor goes after her and tries to help her get a taxi to take her back to her wedding. But while he’s getting cash (Sonic Screwdriver? that’ll do nicely) she manages to borrow money from a kindly stranger. Meanwhile the Doctor spots a scary masked Santa band, just like the one that attacked him before and as Donna speeds off he realises that the driver is another Santa robot! He runs back to the TARDIS and sets off in hot pursuit.

Donna finally realises that she’s in trouble just in time for the TARDIS to fly up next to the Taxi. There follows a very unusual ‘car chase’ with Donna finally jumping from the moving Taxi into the TARDIS.

Unfortunately they end up on the top of a tall building even farther away from the wedding. The Doctor gives her a bio-damper ring to stop the santa robots finding her again, and they sit and talk. She tells him about her job and her fiancé Lance and how he used to make her coffees.

They arrive at the ‘wedding reception’ to find that everyone went ahead and had the party without her. Lance is happily dancing with Neris. Everyone starts bombarding Donna with angry questions so she turns on the tears which works very well.

While the party picks up again the Doctor borrows a phone and starts researching Donna’s employer. Then he notices someone videoing the party and gets him to play back when Donna vanished at the wedding. He recognises the effect, it looks like Huon particles. But that kind of energy doesn’t exist any more, AND it can’t be hidden by a bio-damper. He rushes outside to find the robot Santa band approaching. He and Donna try to find an escape route but they are surrounded. Then the Doctor spots that one of the robots has a remote and becomes suspicious of the Christmas tree. They try to get everyone away from it but then the baubles start to float into the air, very pretty until they start to explode.

The Doctor uses the party sound system to destroy the robots. He leaves with the head of one of them as there is a signal showing that someone is controlling it. Someone up in the sky, and that someone notices and seems impressed. It’s a someone who looks an awful lot like a giant spider.

The Doctor gets Lance to drive him and Donna to H C Clemants. He tells them that it was previously owned by the Torchwood Institute. He also explains that someone has been dosing Donna with Huon particles, which you hardly find anywhere except in the heart of a TARDIS which is why Donna was picked up by his.

They travel down to the unlisted sub-basement of the building. In another surreal sequence the three of them travel along a long, green lit, corridor on Segways. The Doctor climbs up an access tunnel and finds himself on the top of the Thames flood barrier. Exploring further they find a lab where someone has been extracting huon particles. Just as the Doctor assures Donna that he will reverse what was done to her a voice cuts in from the next room and a large steel door rises. Lance slips out the door they came in and runs leaving the Doctor and Donna to be surrounded by robots (minus their Santa disguises this time).

The Doctor comments on a hole in the floor, a very large, very, very deep hole. The Doctor doesn’t want to talk on the intercom and so the one behind all this materialises with them. He recognises her as a Racnoss. The Empress of the Racnoss she corrects.

Lance sneaks up behind the Empress with an axe while Donna distracts her but rather than strike he starts to laugh. He is working with the Empress, he’s the one who has been feeding Donna huon particles. Not only that, when Donna can’t believe that he would to that he goes off on a rant about how stupid she is and what a torture it was to put up with her. He only agreed to marry her so she wouldn’t leave and mess up the plan.

The Empress orders her robots to kill the Doctor but he uses the huon particles in Donna to sumon the TARDIS to materialise around them. Since the Empress didn’t want to tell him what was so interesting at the centre of the Earth he decides to go back to the beginning of the formation of the planet. Donna is still very upset, but standing in the doorway of the TARDIS seeing the early solar system, the Earth as yet unformed, puts it all into perspective.

They find the first rock around which the Earth formed and it’s a Racnoss ship. Back in the present day, deprived of her prey the Empress starts force-feeding huon particles to Lance. The TARDIS is yanked back to the present by the particles but the Doctor manages to land out in the corridor. Unfortunately while he’s searching for something Donna is grabbed and taken back to the Empress.

Donna and Lance are suspended in a giant web above the pit. The Empress orders that the particles be activated and they leave the two humans and descend into the pit where they will reawaken the dormant Racnoss ship and it’s occupants, her children. The Empress drops Lance into the pit to feed her children first because she disapproves of how nasty he was to Donna. She also calls down her ship to attack London.

The Doctor arrives and releases Donna, then he gives the Empress her one chance. He can find her and her children a place to live in peace, but she declines and orders her robots to kill him. This time he has a remote control of his own and deactivates them. Then he tells her the name of his home planet. She’s furious but also frightened, the Time Lords destroyed the Racnoss before and he’s going to do it again. He uses remote controlled exploding baubles to blow holes in the underground complex allowing the river to flood it and pour into the pit where it drowned the Racnoss climbing to the surface.

The Doctor stands there mesmerised by the destruction until Donna calls him. The Empress beams back to her ship where she intends to wreak havoc on the earth, but she’s used up all her energy and is defenceless. Tanks fire on her ship and destroy it.

The Doctor and Donna emerge onto the flood barrier to see that they’ve managed to drain the Thames.

The TARDIS is parked in an ordinary suburban street. Donna emerges. She’s free of huon particles. The Doctor makes it snow. He asks if she wants go with him, but she turns him down, she couldn’t live her life like he does but she thinks he should find someone, someone to stop him sometimes.

At the time this was a one off, the Christmas episode with a very temporary ‘companion’ and there was no reason to expect that we’d see Donna again.