“Torchwood. Outside the Government, beyond the police. Tracking down alien life on Earth and arming the human race against the future. The 21st century is when everything changes and you’ve got to be ready.”

Gwen Cooper is spending an evening out with her boyfriend Rhys Williams. They enjoy a game of bowls (although he’s unhappy when she thrashes him), they see a film at the cinema (although she’s unhappy with his choice and claims she fell asleep), and then go for a drink at a nearby bar. He asks her about her recent secondment to Special Ops, which she’s due to start tomorrow, but she assures him it’s no big deal and her job will mainly consist of filing. They decide to have an early night and are just about to leave when they see what appears to be a plane on fire in the sky above them. Everyone in the area looks up and sees the approaching fireball and it soon becomes clear that this is an enormous meteorite, billowing clouds of smoke in its wake. The meteorite seems to change course and Gwen drags Rhys onto the street to see where it’s going. They chase after it and hear the noise as it disappears over the horizon and crashes to the ground somewhere nearby. Immediately, Gwen receives a text message from Torchwood and tells Rhys she has to go to work…

Captain Jack, Gwen, Owen and Toshiko jump into the car and race through the streets of Cardiff. This is a simple locate and clean-up operation - they need to find that meteorite before anyone else gets their hands on it. Gwen is amazed at the ultra-modern tracking and surveillance equipment they’re using, but she warns them they shouldn’t be hacking into the police computer system. Jack reminds her it’s time she started thinking of herself as part of Torchwood, not the police. They arrive at the crash site only to find that the army are already there and have sealed off the road. Dismissing the army as amateurs, they use their credentials to get through the police cordon and head straight for the command tent. Gwen is the last to enter and is nearly turned away from the restricted area by Private Moriaty and Sergeant Johnson, but Jack vouches for her and rebukes the soldiers for treating her as a little girl. He orders them to leave his team alone while they do their work.

Jack leads Gwen down into a crater where the others are already setting up their equipment around the huge meteorite. Owen has established that it’s bog-standard space debris so they decide to take the usual readings and then vacate the area. The group casually toss each other various bits of equipment and when Gwen is asked to pass Owen a chisel, she does the same - but her aim is poor and the chisel smashes into the meteorite and imbeds itself into the stone. Almost immediately, a strange gas-like substance seeps out and Jack throws gas-masks to everyone. The gas takes the form of what appears to be a sentient energised cloud and then shoots up into the sky. Gwen is mortified.

In an alleyway round the back of a nightclub in the centre of the city, a tearful young girl, Carys Fletcher, is trying to phone her boyfriend Eddie Gwynne. She’s been standing in the club for hours on her own and it’s obvious that he isn’t turning up. She’s sick of his behaviour and wishes she’d never met him. After she leaves a message on his voicemail, she turns to leave and finds herself facing the alien-looking cloud. She’s forced against a wall as the cloud absorbs itself into her body. Moments later, she tries to return to the Night Spot, but is refused admission by the doorman Banksy. She argues that she’s already been inside once and only came out to make a call, but he says they have a no-readmission policy. Without warning, she grabs him and gives him a long and very passionate kiss. She’s allowed back inside.

Inside the busy nightclub, Carys looks around for the right person. That person is a young man she‘s never met before called Matt Stevens, who she approaches and drags straight into the ladies toilet. The other girls in the room swiftly leave and let them get on with things in private, Carys begins kissing Matt. He responds, and within moment they are having sex. As he reaches a climax, his cries of ecstasy turn to screams. There is an explosion of light and Matt is turned into a cloud of golden energy which is then absorbed into Carys. All that remains of Matt at the end is a small pile of dust on the floor.

The Torchwood gang return to the Hub and Gwen can’t seem to apologise enough for her mistake. Jack urges her to stop saying sorry, but the others are less sensitive to her embarrassment. She promises to sort out the problem and hopes that it can’t be anything too serious. On the plus side, they do have some undamaged samples from the meteorite, but on the down side there’s an alien on the loose and they don’t know where it is, why it’s here or what it’s going to do. For Gwen this has been the worst first day ever! Ianto joins them and reports that there’s been a death at a nightclub with unusual circumstances.

It’s the very early hours of the morning by the time the gang arrive at the Night Spot. Jack leads them in, but Gwen holds back when she realises the police office on duty outside is her former partner, PC Andy. She apologises for not calling him, but she’s unable to satisfy his curiosity about her new job. She tells him he might as well go off duty now that they’ve arrived and he’s disconcerted by the fact that she’s in a position to give him orders. Inside, the group examine the remains of Matt on the toilet floor and Jack wonders how the doorman Banksy knew the dust was once a human body. (We then see a flashback scene in which Banksy is masturbating as he watches the CCTV footage of Matt and Carys having sex - and the shock on his face when he witnesses the boy’s fate.) Jack and the others watch the CCTV footage themselves and ask Banksy if he knew who the couple were or had any other information about them. Unfortunately the club gets hundreds of punters every week and he’s not able to tell them anything.

As they leave, Jack gives instructions to the others to select a body from the cryo-chamber that matches the boy’s appearance, then disfigure the face and dump it somewhere remote so that it looks like a suicide. Gwen is horrified to learn that Torchwood keeps a stash of bodies for just such an eventuality. She’s worried about the boy’s family, but Jack points out that they can hardly tell them what really happened. He traces the elements from the crash site and it leads them to the alleyway behind the Night Spot. He also notices another CCTV camera on the street, and later they watch the footage of Carys being taken over by the alien gas. Gwen sadly realises that the whole thing was her fault. The boy would still be alive if it hadn’t been for her actions at the crash site. She’s determined to make sure the girl doesn’t kill again…

Carys has returned home, but she appears to be in a state of shock and is oblivious to the conversation her father Ivan is having with her. He thinks she’s probably just hungover from the night before, but she says she can’t remember. Later, she breaks down in tears as she takes a shower.

Back at the Hub, Jack is using satellite tracking data to determine the inward trajectory of the meteorite. Gwen observes that it’s a sort of route planner, similar to the job her boyfriend does. This is the first time any of her new colleagues realised she had a boyfriend, and when Gwen asks about the others she discovers they are all so involved in Torchwood that none of them have partners. She wonders how they switch off from their work if none of them have time for a personal life, but they don‘t really have an answer for her. Owen starts work on analysing the gases from the meteorite while Toshiko uses a computer programme to try to find a match for the CCTV footage of Carys. Gwen is once again concerned that Torchwood has a photographic database of everyone in the UK and Jack has to remind her that she is now part of the group too. Unfortunately the footage isn’t very clear and the computer can only narrow the search down to 119 possible matches. Ianto offers to cross-check all 119 suspects manually, but Jack suggests Toshiko search for CCTV footage from other street cameras to see if they can find the moment earlier in the evening when the girl first arrived at the nightclub.

As Carys sits in her bedroom, she starts to suffer from terrible spasms. The doorbell rings and it’s the postman with a package. She grabs him, drags him inside the house and begins seducing him on the bed. At that the moment the door is kicked in and the Torchwood gang burst into the room, fully armed and kitted out with gas-masks and protective suits. At gunpoint they order the postman to get dressed and leave. When they’re alone with Carys, Toshiko checks the air and confirms it’s safe, but as they remove their gas-masks, Carys takes the opportunity to escape into the hallway. Fortunately, Owen is prepared for her and as she runs past, he drops a strange metal device to the floor in front of her. She finds herself trapped inside an alien force-field which Owen describes as an inflatable cell. They have to work quickly as the battery will only power the cell for about an hour. Even though he stopped their prisoner escaping, Owen is still rebuked by Jack for bringing alien technology out of the Hub.

The group return to their base and Gwen is asked to interrogate their prisoner. She locks Carys into one of the underground cells and is surprised when the girl appears to know nothing about what happened the night before. She can’t understand why she’s been arrested as she’s never been in trouble before. Gwen tells Carys there’s something living inside her and suddenly the girl goes into spasms again and is hurled against the walls of the cell. Possessed by the alien, Carys accuses Gwen of breaking her ship. Gwen warns her she will not be allowed to invade or enslave the human race, but the alien has no such intention. All it wants is the energy drawn from the sexual climax - it feeds off orgasms. Carys is again thrown against the walls, and concerned for the girl’s safety, Gwen opens the cell door and rushes in. Temporarily restored to her normal self, Carys begs Gwen to get the creature out of her, but as she helps her prisoner to her feet, there is a sudden mutual attraction and the two women start to kiss.

In the main lab, Owen spots what’s happening on the internal CCTV screen. After watching for a few moments (and setting the video to record, of course) he alerts the others to what’s happening. They’re all transfixed for a second before realising they ought to get Gwen out of there. The alien inside Carys rejects Gwen’s advances, claiming she can only feed off men. Gwen suddenly realises what she’s done and backs out, rather embarrassed. Before the alien takes control of her again, Carys makes Gwen promise that she’ll help her. At that moment, Gwen’s mobile phone rings and it’s her boyfriend Rhys checking up on how her first day at work is going. Losing concentration for a moment, Gwen backs up against one of the cell doors and is attacked from behind by the Weevil. She returns to the lab and gets a round of applause from an excited Owen. Gwen is furious and attacks Owen physically and verbally for treating Carys’s situation as a joke. He reminds her that the girl in the cell downstairs is a murderer. Just then, Ianto arrives with the dinner.

The five of them enjoy a meal in the boardroom and swap amusing anecdotes about their past experiences with aliens. When Jack pops out for a moment, the group question Gwen about what she knows of their leader. They were banking on her training as a police officer to find out who he is and where he’s from. They know nothing about him at all, but each of them seems to have their own theories. Owen thinks he must be gay and Ianto suspects he’s former CIA. Whatever the answer, Gwen is sure Jack must have good reasons for wanting to keep his details secret. They’re interrupted by the sound of Carys sobbing, alone in her cell. Gwen is horrified at the thought that they’ve been enjoying dinner while the girl downstairs is fighting for her life. Jack returns and assures her that they’ve been busy. The computers are running a full bio-scan, profiling her body to see what effect the alien’s having on her, and also taking samples of the air in the cell so they can analyse any changes in the environment around her. But Gwen realises they’ve all been hidden down here too long. They’ve spent so much time chasing aliens they’ve forgotten what it’s like to be human. Jack challenges her with the job of reminding them.

Gwen spends the next few hours in the lab alone, preparing a full history of the life of Carys Fletcher from baby to young woman, including medical records, school reports, personnel files from her employers, swimming certificates, details of her mother‘s death in a car crash ten years ago, and a collection of emails discussing the merits of Orlando Bloom and Heath Ledger. Later, she gives a presentation to Jack and he’s forced to realise the problem they face is not about meteorites or gases. It’s about a desperate girl who needs their help. They need to remind Carys who she is and give her enough support to keep fighting. For once, Jack is almost speechless, but he thinks Gwen is brilliant. At least he does until she suggests bringing Carys’s dad Ivan in to see her. He argues that their priority is to contain the alien threat, not put civilians at risk, but she reminds him that no one else is going to help Carys.

The others have been busy too. Toshiko has the results of the air analysis which proves that the alien is secreting a powerful blend of airborne sex pheromones, thousands of times stronger than you would normally experience, making Carys a walking aphrodisiac. Gwen realises this is why she was so attracted to the girl when she was in the cell with her. This also means no man can possibly be let anywhere near her. They suddenly remember Owen was working in the cellar, and they rush down to discover Carys has gone and Owen is locked up in the cell, naked and feeling a bit of a thingy.

Carys tries to escape from the Hub, but is confronted by Jack. There is a face-off and both end up arming themselves with objects from around the laboratory. Suddenly Carys grabs the glass container holding the severed hand. Jack becomes almost desperate in his attempts to prevent her from damaging the specimen, saying it’s worthless to anyone but him. He threatens to shoot her, but she calls his bluff and backs into the lift. Jack races up the staircase to ground level and catches up with her just as she bursts into the tourist information office that leads out onto the street. Ianto is there and Jack tells him to open the door so she can escape. But when he asks Carys to give him the jar, she smashes it to the ground instead and flees while his attention is on the disembodied hand. Gwen and Toshiko arrive and race out into the street, but it’s too late - Carys has disappeared.

Back in the Hub, Gwen wants to know why the hand is more important to Jack than saving Carys’s life, but all he will say is that she should make herself useful by using her police contacts to track the girl down. Owen calls the group together to demonstrate a discovery he’s made. He’s been trying to interpret the results of the bio-scan, but there were no definitive readings as Carys’s metabolism keeps changing as she fights again the alien trying to control her body. Instead, Owen had tried to recreate the circumstances by accelerating the process to see what will happen to Carys. He’s infected a rat with the two gas traces found at the crash site and discovered that once they start to flow around the body the heart rate triples, the brain swells and presses against the skull, the lungs begin to shrink making it impossible to breath and the pressure increases on all the internal organs until - the rat explodes!!! Rat jam!

Carys explores the streets of Cardiff, looking for suitable men. Gwen is trying to think like Carys, to put herself in the girl’s position and work out what her next move is likely to be. The overriding instinct for the alien is to try to have sex in order to survive, but Carys knows that whoever she has sex with is going to die - so what would she do? The likely possibilities include brothels and lap-dance clubs, but it‘s Toshiko who knows what she would do if she were in Carys‘s position…

Carys arrives at her ex-boyfriend’s flat and demands to see him. Eddie is unhappy about this as his partner Bethan could have been home. He complains about the message she left on his mobile the night before and reminds her that he never had any intention of leaving Bethan. She threatens to kill him, then starts to suffer from the terrible spasms again. She asks if he ever loved her, but his answer is no. She tells him that he could have saved himself if he’d given a different answer - and then she jumps on top of him. Later, Jack and Gwen burst into Eddie’s flat and find just a pile of dust on the bed. So where will she go next?

The group drive around, trying to work out their next move. Gwen suggests putting bromide in the water supply, but Jack says it’s too hit and miss. In any case, the water company got really pissed off last time they tried that. As Gwen did a profile on Carys, they ask if there’s anything she knows that might give them a clue, but she can’t think of anything. Toshiko calls up her employment record and they discover she’s working as a temp at Conway Clinic, a sperm donor/fertility clinic where an unlimited source of young men can be found. As they race to the scene, Gwen is handed a gun…

Carys arrives at the Clinic and tells the receptionist that ‘it’ needs to deed and the energy she’s been absorbing for it is not lasting very long. She knocks the woman out and then calls the waiting room, summoning each of the men there one by one to a side room where she will be waiting for them.

Toshiko has deduced from their tests that the alien has taken a human host because prolonged exposure to Earth’s atmosphere would be poisonous to it. If they can isolate it from Carys’s body, it shouldn’t survive for long. They arrive at the Clinic and race inside, drawing their weapons and kicking open the door. They order all the remaining men in the waiting room to leave and then start searching the building. In every room they find the same thing, just a small pile of dust is all that remains of the men. Eventually they manage to corner Carys, leaving her nowhere to run. The strain on her body becomes too much and she collapses to the floor in agony. The alien in Carys tells them that each time the host has sex, the effect of the energy it absorbs becomes less and it’s becoming steadily weaker. Carys begs them to help her feel human again, but there’s nothing anyone can do. Except for Jack. He claims he has a surplus of ’alive’ and he’s giving it away. In front of the others, he bends down and kisses Carys. Energy flows between them and Carys passes out. Gwen offers her own body as a host and implores the alien to leave the young girl. However, it’s a trick and when the alien comes out of Carys’s body, Jack throws down the metal device that Owen used earlier and the gas cloud becomes trapped inside the force-field. Owen is worried about how much longer the battery will last for, but luck seems to be on their side for once and the alien slowly dies in the atmosphere and ends up as nothing more than another pile of dust on the floor.