The Doctor splutters that it is physically impossible for the woman to have made her way inside and reveals to her that she is inside the TARDIS. Aggressively she moans that he is making this up before theorising that her friend Nerys must have hired him to kidnap her. As he pokes at the controls of the ship she explains that she was half way up the aisle when she was taken and threatens to sue him as soon as she is married.

She then runs to the doors across the gangway and before the Doctor can warn her she thrusts them open, stunning herself at the glowing orb of light before her. The Doctor explains that she is in outer space in a ship called the TARDIS, protecting her from the vacuum outside via a force field. He introduces himself and she reveals that she is called Donna Noble. She soon realises that he is an alien before complaining of a draft being let in by the open doors. He closes them and returns to the console, still claiming that her appearance within the ship is impossible. He begins to examine her and theorises what may be wrong, before she slaps him and tells him to get her to the church.

Becoming defensive he claims he does not want her with him anyway, and sets the controls for the exact location the wedding, in Chiswick. Donna then spots a discarded blouse draped over a handrail nearby, and takes it as evidence of other girls the Doctor has taken. The Time Lord sees the blouse and claims it belonged to one of his friends, whom he has lost. He continues to programme the controls and takes the top back.

In the church disarray runs rampant. Donna’s mother calls frantically on the phone for people to help find her, and then asks the groom Lance if she has been seen. He admits she is missing and after the mother chides her daughter for showing off she worries that she could be dead.

The TARDIS has landed and as Donna walks outside she is astounded to find that they are not at the church. The Doctor wonders what is wrong with the ship and asks Donna if she has knowledge of anything that may have caused her apparition in his ship. She does not respond and is instead fascinated by the fact that the ship appears to be bigger on the inside than the outside. Examining both dimensions she begins to run, and tells the Doctor to leave her alone. She examines her watch and explains they are late. The Doctor asks if she has a phone but angrily and sarcastically she notes that her wedding dress has no pockets. He wishes her futures husband good luck before listening to her vow that no Martian is going to ruin her big day. The Doctor tries to explain that he is not from Mars before joining her in trying to hail a taxi. After realising that passers by are supposing she is either in fancy dress, drunk or in drag, Donna sighs, but the Doctor solves the situation by whistling inhumanely loudly. A taxi stops and they get inside, but are soon thrown out again when they realise they have no money.

Back on the pavement the Doctor realises that it is Christmas and as Donna heads for a phone box the Doctor tries to get hold of some money. Arriving at a cash point he waits frantically for his turn. Donna reaches her mother but the battery cuts out and Lance has no signal. Donna leaves her mother a message, but cannot explain where she is, citing that the only certainty is that she is on Earth. The Doctor meanwhile uses the sonic screwdriver to retrieve some money, and as Donna urges a passer-by to lend her some money he notices a series of sinister figures looming nearby; a group of masked Santa’s playing Christmas carols on brass instruments.

Donna climbs inside the cab and claims that she will see the Doctor in court. The Time Lord realises that the cab is being driven by one of the Santa’s, and another on the street is raising it’s musical instrument to try and fire the weapon concealed inside at him. Creating a distraction, the Doctor uses the Sonic Screwdriver to make the cash machine fire out money and as the passers by try and grab the bank notes the Doctor makes his escape.

In the cab Donna asks the driver to hurry and then realises that the driver has missed the turning, they are going the wrong way. The Doctor meanwhile returns to the TARDIS and begins to activate the controls and as Donna cries for the cab driver to turn the taxi around, she reaches forward to pull his hood, revealing a robotic face behind the mask. She tries to open the taxi doors but they are locked, as are the windows and soon she is screaming for help. The Doctor frantically pilots his ship and as the console whines out TARDIS makes its entry onto the motorway, hovering alongside the taxi as it speeds along the tarmac.

He unlocks the doors with the Sonic Screwdriver and then urges her to jump, but the taxi speeds away. Pulling on a length of string he has attached to the controls he begins to pilot the ship in order to catch up, the console sending out showers of sparks in protest. Soon he is confronting the bride again and after much persuading, from the Doctor and other passengers in passing cars, the Doctor explains that for whatever reason the robot needs her, and it will not be good. She opens up the door and nervously hovers inches above the road surface. The Doctor tells her to trust him and she asks if that is what he said to his lost friend. Sorrowfully he admits that she did trust him and moments later Donna leaps into his arms.

Some time later the TARDIS sits on a rooftop, the Doctor cooling the ship down with a fire extinguisher. Donna admits that they have missed the wedding, before wishing that they had a time machine so that they could go back and make things right. The Doctor explains that even if they did he couldn’t cross someone’s own personal timeline…apparently. Donna strolls off and he removes his coat, placing it over her shoulders to keep warm. They sit together on the rooftop and he gives her a ring, explaining that it is a biodamper; it will keep her hidden from the creatures that are after her.

The Doctor begins to explain that the robotic Santa’s are scavengers, using costumes to blend into surroundings. He claims to have met them the Christmas before and following Donna’s bemusement recounts the spaceship hovering over London on Christmas day, when Donna had a hangover. He remembers spending Christmas on the Powell Estate, but those he spent it with are all gone. Donna asks who his friend was but he instead wonders what the robot mercenaries want with Donna and how she got into the TARDIS. He begins to examine her with the Sonic Screwdriver and finds nothing special, so asks her about her job.

She explains that she works as a secretary at a firm called H R Clemens, and it was then, six months ago that she met Lance. She explains that he insisted they get married and nagged her into submission, but in reality it is shown to be the other way round. After explaining that the company works in identification procedures, the Doctor ponders about the importance of keys, before his would-be companion admits that it is time to face the consequences of her disappearance, and the Doctor can do the explaining, the guests must be heartbroken.

At the reception venue everyone is dancing to upbeat songs and as Donna enters with the Doctor all goes silent. Furious at her being left out she confronts Lance and the Doctor quickly introduces himself, as Donna’s mother appears, asking what happened. Soon everyone is talking at her at once and she begins to sob, causing a wave of sympathetic cries and applause. However as she hugs Lance she sneakily turns her face to the Doctor and winks.

Some time later the music resumes and Donna begins to enjoy herself, leaving the Doctor at the bar, examining a mobile phone. Zapping it with the Sonic Screwdriver he finds information held on H R Clemens, and finds that its soul proprietor is Torchwood. He puts down the phone and as he looks on at the dancing couples he is reminded of Rose, and his eyes begin to well up. Soon however he is busy again, asking the cameraman of the wedding to replay the video of the ceremony. As he watches he sees Donna glow with golden energy, recognising it as a cloud of Huon Energy, something that has not been around for billions f years, so old that it cannot be hidden by a biodamper.

He rushes to a window to see the robotic Santa’s advancing and then returns to Donna to tell her she must leave. Soon they realise that the house is surrounded, and as one of the robots lifts a remote control the Doctor realises their plan. He orders everyone to step back from the Christmas trees lining the room and as the disbelieving crowd do a she says, the barbules hanging on the branches glide into the air, floating around before launching forward and exploding like grenades. Tables collapse and people run for cover as the robots enter the room and prepare to open fire.

Before they can attack, the Doctor stands up and addresses them, warning them not to let a man near the sound system when he is armed with a Sonic Screwdriver. He brandishes the DJ microphone and then fires the sonic device into the mixing desk, creating piercing screech that destroys the robotic assailants. As Donna tries to help the fallen guests the Doctor realises a second remote control is hidden in the robot’s helmets, they are no longer scavengers, they are being used by something else. Donna asks him to help the injured guests, but he claims that he must look at the bigger picture. In a fit of realisation he bounds away and after her mother asks who the stranger is, Donna runs after him.

Outside, the Doctor realises that whatever is controlling the robots is up in the sky, and in a dark control room a large claw points at his picture on a screen. A rasping voice declares that the Doctor and the bride shall soon come to her. From a giant web in a ship made of the very fabric of a spider’s abode the voice of a giant fanged mouth declares that soon it will descend upon the Earth and shine.

Meanwhile, the Doctor decides he must return to Donna’s office at H R Clemens to see where it all started and he decides to take her and Lance with him. Once there the explains that the company was brought out twenty three years ago by the Torchwood Institute, the administration behind the battle of Canary Wharf, which Donna seems oblivious to as she was scuba diving in Spain. He explains that although Torchwood was destroyed H R Clemens has remained in business, suggesting that someone else is behind the running of the company.

Donna asks why she is so important and the Doctor explains that she has been dosed with Huon energy, which has not existed since the dark times and is only found in the TARDIS, which explains why Donna appeared in the TARDIS, the two sets of Huon particles activated at the same time and magnetised. He then accesses the official building plans of the building on a computer and realises that there is a floor missing from the plans that can be accessed via the lift. Together with Donna and Lance they descend down in the lift and the sinister creature in its spaceship monitors their progress. The bride is approaching and she is the key.

Arriving in the underground level the Doctor and his accomplices begin to make their move and use motorised transporters to move along the vast corridors. They arrive at a locked door and the Doctor manages to open it, ascending an iron ladder that leads him away from the others. He finds himself at another hatchway and with some effort he pushes it open, finding himself standing on top of the Thames Flood Barrier. He returns below to tell Donna and then proceeds to a vast laboratory chamber, full of particle extrusion machinery.

The Time Lord explains that whoever is in charge is manufacturing Huon particles, after his own people destroyed them by unravelling their genetic structure. He tells Donna that the particles are inert, but need a human body to saturise them. In a fit of excited realisation he explains that during the wedding Donna’s body was alive with hormones, chemical signals that helped to cook the Huon particles. Donna slaps him again for appearing so excited at her troubles and then asks if the particles inside her are dangerous. He admits that they are deadly, but he promises to reverse what has been done, he is not about to loose someone else.

Suddenly a rasping voice calls to them and one of the walls of the laboratory slides away, revealing a deep pit and hoards of the unmasked Santa robots, armed and ready to fire. The voice tells them that Donna has been long since lost, and that it has waited for so long, hibernating at the edge of the universe until the secret heart was uncovered and called out to it. As the voice talks Lance begins to sneak away, running along the corridors and into the hatchway.

The Doctor inspects the pit and the voice tells him that it reaches down into the centre of the Earth. The Time Lord then goads the voice into revealing itself and soon the creature fades from its ship high above the planet’s surface and appears before them. It is an enormous spider-like creature, blood red with sharp fangs and a face dotted with inhuman eyes. It hisses and spits and bears its long feet, before the Doctor recognises it as one of the Rachnoss race, the Empress.

He ponders if she is the only one, and explains to Donna that the Rachnoss were born in the dark times, and were known as omnivores that devoured whole planets, along with their inhabitants; indeed he points out the trapped body of H R Clemens himself in the web above the Empress’ head. He continues to explain that the Rachnoss were wiped out by the very first civilisations, but the Empress cuts in to explain that she survived. Donna addresses the creature before her and asks why she has been filled with the Huon particles, but soon begins to try and buy time when she sees Lance creeping up at the Empress with an axe. She calls to him to strike her and he makes a swing, but stops and begins to laugh along with the giant spider.

The Doctor apologises to his friend but she can’t understand, and when he reminds her that she first met Lance when he made her a cup of coffee, she realises that he has been poisoning her for the past six months. A dumbfounded Donna listens as Lance gets off his chest his pent up hatred for Donna, the trivial life she has led him into in the run up to the wedding. As the bride mutters that he loved him he merely points out that it was that which made it so easy to fool her.

The Doctor asks why he did such a thing and he explains that it was his chance to see the wonders of the universe, to see the sights that make the human race look so small. The Time Lord tries to find out why the Empress has had the pit dug when all of her people were wiped out, but she and Lance note that they do not need him, he can be killed. As the robots take aim the Doctor realises that if Donna can be drawn to the TARDIS, then the process can be reversed, and as the robots prepare to fire he uses the uses a vial of Huon particle to materialise the TARDIS around them.

Soon the ship is materialising and the Doctor admits that the ship can in fact travel in time, and explains that they must find out why the Empress is digging to the centre of Earth. He looks over but Donna is not listening, she is shaking with tears. Meanwhile, the Empress theorises that if her key has been lost, then a new one must be cut. She signals to her robots and they turn on Lance.

In the TARDIS the Doctor explains that they have arrived and moves to open the doors, revealing another starscape, at the point when the Earth was first formed. Donna looks at the mass of rocks floating around and thinks about how insignificant the human race seems, but the Doctor tells her that humans are meant to be that way, making sense out of chaos by marking life out with weddings and other events.

In the distance a giant ship appears from within a cloud of dust, the one rock that will form the centre of everything, the Rachnoss’ ship. Back in the basement, the Empress observes as the robots force-feed Lance the liquid Huon particles, cutting the new key. In the TARDIS the Doctor and Donna watch as the Earth forms around the Rachnoss ship, but are forced into turbulence as the Empress tries to pull them back, whilst ordering her servants to bind Lance, who is now glowing with Huon energy.

Suddenly the Doctor has an idea, he picks from the floor the wired-up extrapolator, and uses it to materialise the TARDIS out of the pull of the Rachnoss, back into the corridor leading into the base. The Empress calls for the robots to find Donna and as the Doctor inspects the walls of the corridor he explains to Donna that the Huon particles inside her will enable the Empress to unlock the web at the centre of the Earth in which the Rachnoss are entombed.

As he talks he is unaware that Donna is abducted, grabbed by the robotic servants and taken away. However when he notes the sudden silence he rushes to find her again, only to be confronted by one of the robots, armed with a gun. Meanwhile Donna finds herself tangled in the web with Lance and as the Empress taunts them she orders that the particles be activated and purged. As she talks the two bodies begin to glow, and the golden mist descends into the pit, to awaken he children and release them onto Earth to feast on flesh.

She calls her ship, the Webstar; to descend onto the Earth and as it enters the atmosphere the Empress severs Lance from the web, leaving him to fall into the pit. The ship descends the streets of London and zaps bolts of energy onto the ground, attacking the defenceless bystanders. As events unfold one of the robots begins to return to the base, but the Empress realises the disguise and order the Doctor to unmask himself. He does so and then fires the Sonic Screwdriver at the web, forcing it to loosen its grip on Donna. She swings down to him on a tendril of web but her jump is misjudged, she lands too low for the Doctor to catch her and with a thud, land son the floor, thanking the Time Lord for nothing.

The Doctor turns to the Empress and offers her one last change, explaining that he can take her and her children to another planet to live and end the carnage on Earth. She declines it he announces that what happens next is her own doing. She tries to rally he servants to fire on the Doctor but he orders them to relax, causing them to run down. He shows Donna the remote control he took at the reception when the robots attacked and explains that he kept it in his pockets, pointing out that they are bigger on the inside.

The Empress announces that she does not need the droids; her children can feast on the Doctor’s Martian flesh. He cuts in and explains that he is not from Mars, his planet is far away and long since gone, but it’s name lives on. Gallifrey. The Empress hisses and remarks that it was the Gallifreyans who slaughtered the Rachnoss. The Doctor warns her that it was she who did this and he reveals a set of the barbules that exploded at the wedding reception. He uses the remote control to fire them at the walls of the base, letting the water of the Thames flood in, deep down into the pit. The Empress calls out to her children as they screech out in pain and Donna tells the Doctor that he can stop now, but he remains silent, a stony expression on his face.

As the water continues to flood the two friends manage to make an escape and the Empress beams back to the Webstar, but as the Doctor points out, she has used up all of the Huon energy, and is now defenceless. Outside a gigantic tank rolls into the street, a radio voice reporting that Mr Saxon has given orders to fire at will. The barrel releases a missile that launches up into the skies, colliding with the Webstar. As the Empress cries out in agony and the Doctor and Donna find themselves back out in the open air on top of the Flood Barrier, the web of the ship begins to unravel and fiery explosions rip across the framework, leaving the sky empty one more and the Doctor and Donna to remark at their triumph, with only one problem remaining; they have drained the Thames.

Some time later the TARDIS stands on a street corner in the dark of night. The Doctor and Donna appear from within, and the Time Lord explains that all of the Huon particles have gone. Donna however is not so jubilant, she wallows in the fact that she has lost her job, missed her wedding and almost become a widow all in the same day. The Doctor tells her that he couldn’t save Lance, but Donna claims that he deserved it, before retracting her words with one look from the Doctor. She glances inside one of the houses, and sees her worried parents hugging each other amongst the Christmas decorations.

The Doctor remembers how Donna once told him that she hated Christmas and to try and cheer her up he activates a button on the TARDIS exterior, sending a bright light up into the air, which explodes and sends a shower of snow down upon them. Donna smiles and laughs as the Time Lord explains it is a simple atmospheric excitation. Donna sighs and wishes him a merry Christmas, a sentiment he returns before momentarily falling silent. He asks her what she will do now everything is over, and she tells him that she wants to travel, see more of Earth and go out to do something with her life.

The Doctor ponders and tells her that she could always go with him, but she claims that she cannot. He sheepishly agrees with her and she tells him that she couldn’t live a life as the Doctor does; despite the beauty there is always terror. She remembers the screaming children of the Empress and how the Doctor merely stood and watched, and now he’s managed to make it snow; he scares her.

The Doctor, noticeably disappointed, shuffles her feet and Donna tells him to come in for Christmas dinner. He agrees and explains that first he must properly park the TARDIS as she warns her parents that he is coming. However when she turns her back the ship’s engines start to whine and she calls out his name. The noise stops and he reappears, complaining of her shouting. She asks if she will ever see him again and he tells her she will if he is lucky. She asks him to promise her that he will find someone. He claims that he does not need anyone but she tells him that he does, sometimes he needs someone to stop him. He quietly agrees before thanking her and tells her to be magnificent.

He makes to leave but she has one more question for him. She asks what the name of his lost friend was and with his eyes already filling with tears he tells her she was called Rose. He closes the TARDIS door and moments later the ship rockets into the air and disappears, leaving Donna to turn and walk away.