Emma Webster is a perfectly ordinary woman who posts about her relationship woes on Facebook, goes jogging for exercise, has signed up for speed dating, and doesn't really enjoy herself at work. One night, while jogging and listening to Girls Aloud on her iPod, she sees a perfectly beautiful woman who appears to have washed up on the beach. The woman is holding a strange device, and when Emma picks it up, it speaks to her telepathically in the voice of Cheryl from Girls Aloud. The device claims that the other woman is just someone who got it ashore; she will soon wake up, go home, and forget that all of this happened. In the meantime, the device offers to make Emma's life better. Emma takes the device home with her, and immediately notices a difference; she is still herself, but a taller, trimmer, and more perfect version. Few people notice the change immediately, and her workmate "Vile Kate," as usual, finds exactly the right "compliment" to make Emma feel terrible about herself. The voice in her head offers to give Vile Kate cancer, but Emma turns down the offer; nevertheless, she believes the voice when it tells her that everything's going to change for her now.

Ianto awakens to find that he has somehow become a woman -- a perfectly beautiful woman with nary a hair out of place. He/she manages to convince Jack and Gwen of her identity, and Jack gives her an anti-retcon pill that should enable her to remember how she became a woman (as well as every single thing that's ever happened to her in her life). While Ianto grows accustomed to her new body, Gwen and Jack investigate another incident that occurred last night; the ferry between Cardiff and Dublin has been torn apart as if it ran into a mine, but none of the survivors can remember how it happened. PC Andy then calls Gwen to a restaurant named Abalone's, where a male skeleton still dressed as if for a date has materialised out of nowhere. Gwen accidentally smashes the skeleton to dust while trying to retrieve its mobile, but Ianto is able to trace the mobile's owner: Patrick Matthews, a young man who works at Brenda's chip shop and who is still very much alive. Patrick thinks that the female Ianto is trying to chat him up and asks her out on a date, claiming that he's already booked a table at Abalone's for next Saturday's speed-dating event. Patrick is probably doomed to die in the future, and it may not be possible to save him if that means changing history. Gloomily, Ianto hails a cab and leaves the chip shop, but as she goes, she notices a man staring at her as if he's seen a ghost.

A mass group of skeletons materialises in a bar called Tomboli's. All of the skeletons are male, and they are all physically perfect, even down to their teeth. Jack has also detected an increase in static electricity across Cardiff, which seems like the least of their problems until he hears of another incident at a car park. He demonstrates the problem to Gwen and Ianto by rubbing a balloon in his hair and releasing it; it rises three metres, and then explodes. The static charge is just one element of an energy field blanketing the city; the people of Cardiff are beginning to have trouble sleeping, Jack is developing pimples, and like the skeletons at Tomboli's, the cars in this parking lot have all been reduced to powder -- along with the couples who were making out in them at the time. The field has been building ever since Sunday, which is the night that Ianto changed into a woman.

Emma has become physically perfect, and she gives in to temptation and allows the device to undo all of Kate's recent cosmetic surgery and cause her to put on weight. It's getting to be a bit much for her, but the voice keeps urging her to get out there and live life to the fullest. She goes out to a bar, where a man named Joe approaches her on a whim and chats her up; she likes him, but he's not quite perfect, so the voice offers to tweak him a little. Joe immediately quits smoking, becomes a bit taller, and reveals that he likes all of the same films that Emma likes. They spend a perfect night together, but Emma realises that it's too perfect; Joe no longer seems to have a personality of his own, and does nothing but agree with her. The voice offers to chalk this one up to experience and ensure that Joe never bothers her again, and Emma dumps Joe, who walks out to the pier and sits there alone, crying, until his body disintegrates and the rain washes him away.

Ianto convinces Patrick not to go to the speed-dating event he'd planned, and Gwen takes his place, hoping to find out what would have happened at the event to send his disintegrating skeleton back in time. Rhys finds her dressing up for a night out, and when she explains what she's doing, he insists upon going with her. Gwen loses the argument and allows Rhys to accompany her to Abalone's, where a few rounds of speed-dating convinces them both that they're lucky to be out of the singles scene. But then Rhys sits down with Emma, and finds himself telling her all about how he came to the event to get over his ex. Emma is charmed by Rhys's honesty and innocent friendliness, and Rhys finds Emma to be almost perfect. Gwen laughs off her jealousy as they leave, but as soon as Rhys falls asleep that night, she heads straight to the Hub and looks up Emma Webster on the Net. Her recent photographs indicate that she's had an unnaturally quick makeover -- and the next day, when Rhys gets out of bed, he appears a bit taller, trimmer, and fitter. He's still himself, but almost perfect. Gwen is now convinced that Emma is dating her way through Cardiff's singles scene, making over those who attract her attention and killing them when they prove less than perfect; indeed, the skeletons at Tomboli's are from another speed-dating event, at which Emma got bored and told the voice in her head to send everyone away. Rhys still insists that he's taking this seriously as an undercover assignment, but he seems a bit too excited when Emma calls him to ask him out on a second date. Gwen vows to keep an eye on him for his own good.

Back at the Hub, Jack discovers that, before Owen's final death, he created a computer program to trawl through recent news reports looking for suspicious health-care initiatives. One night, while Gwen and Jack were out hunting Weevils, the program brought a flagged report to Ianto's attention. The Cardiff-Dublin ferry had been hosting a series of health-care seminars for a company that promised miracle cures beyond the reach of science -- and in one of the news photos, a woman who looks just like Ianto does now is standing with the other "Hope Boat" passengers. As Ianto thinks about the ferry, her memories begin to return...

Before: Ianto boards the Cardiff-Dublin ferry to investigate the Hope Boat news report, and ends up being roped into a hen party for a young woman called Lucky Debbie, who is engaged to a man named Phil. Debbie tries to set Ianto up with her friend Kerry, but Ianto slips away from the celebrations when he learns of a "health presentation" being held in the cinema. A good-looking man and woman watch from the back of the movie hall as the ill and elderly visitors watch a video promising a non-invasive procedure that will cure whatever ails them. Ianto tries to avoid suspicion by spending the day in Dublin with Debbie and Kerry, and after Kerry drinks too much and passes out, Debbie admits that she knows Kerry slept with Phil. Back on the ferry, Ianto is invited to an interview with the good-looking woman, Christine Kielty; still a bit tipsy himself, he blurts out that he's lost his girlfriend and two close friends recently, and that he wants the grief to stop. Christine promises that she can take away all his pain, but is deliberately vague about what the procedure entails. Ianto hides outside the room after his interview, and overhears Christine's husband Ross promising an elderly couple that he can cure the woman's Parkinson's disease.

Ianto heads up to the deck to think things through in the fresh air, but sees a fog bank closing in around the ship as if cutting it off. Two glowing figures then descend, tear through the ferry's hull as a demonstration of strength, and threaten to start killing passengers unless Christine and Ross return what they've stolen. One of the figures then casually asks the terrified passengers for a cigarette, and when Lucky Debbie hands one over, the figure promises to kill her last. Realising that the figures aren't bluffing, Ianto offers to lead them to the Kieltys. Ross has fled, but Christine is hiding in the cinema. The figures are unable to take the device from her unless she gives it up freely, so they set her on fire as Ianto watches helplessly. The device repairs Christine's body as quickly as it burns, but the pain is intolerable -- and rather than surrender the device to the two figures, she tosses it to Ianto while it's still working to repair her body based on its recorded template. Unsure what he's doing, Ianto runs for it and jumps off the sinking ferry; as he does so, he thinks he catches a glimpse of Lucky Debbie being struck down by a snapping steel hawser.

Now: Ianto still doesn't remember what happened after he/she jumped off the ferry, but now that she remembers seeing Ross Kielty, she knows he's the man who was staring at her outside Brenda's chip shop. Jack and Ianto track him down, but his delight at seeing Christine alive again is short-lived when Ianto tells him what really happened. Broken, Ross explains that he and Christine used to be interior decorators, and that they found the alien device on the mantelpiece of a gay couple they were doing some work for. Christine impulsively stole it when it spoke to her, offering to make their lives perfect; once they were satisfied, they tried using it to help others. Jack can't tell Ross whether or not he did the right thing, and Ross must watch helplessly as Ianto apologises and walks away in his wife's body. Back at the Hub, however, Jack reveals that he now knows what's going on, and that it's his fault. He leaves the Hub, refusing to explain himself but telling Ianto to keep an eye on the energy field, which will go critical in about a day's time.

Emma is preparing for her date with Rhys when Gwen shows up at her flat. All Gwen wants to do is have a word with her, but as far as Emma is concerned, Gwen must be Rhys's psycho stalker ex-girlfriend, and the world would be more perfect without her in it. Gwen becomes invisible and intangible, and is frozen in place, slowly fading away to nothing like the women from the speed-dating event at Tomboli's. Rhys picks up Emma for their date and has all but forgotten Gwen when they return to Emma's flat; however, as Emma invites Rhys to bed, Rhys catches sight of Gwen's handbag lying on Emma's sofa and remembers why he's here. Emma claims that Gwen showed up raving and then left, but Rhys reveals that Gwen is his wife and demands to know what really happened. Desperate, Emma pulls the device out of her purse and shows it to Rhys, claiming that it can make their lives perfect, but he snatches it from her hands before she realises what he's doing. Rhys uses the device to bring Gwen back and to freeze Emma in place, turning her back to the ordinary woman she used to be. The device is speaking to Rhys with the voice of David Beckham, but he resists temptation and gives it to Gwen, telling her that Jack will know what to do with it. When Gwen returns to the Hub, however, Ianto reveals that Jack has been missing for 12 hours -- and Ianto then takes one look at Emma's device and recognises it as the thing that Christine tossed to him on the ferry.

Three years ago, Jack encountered two young men named Brendan and Jon, who were too perfect to be anything but alien. They called themselves the Perfection and claimed to be gods, but insisted that rather than using their powers to make the world perfect, they just wanted some quiet time improving the gay scene in Cardiff. Jack agreed to leave them alone on the understanding that he'd come for them all guns blazing if they betrayed his trust. He's only seen them once since, during an incident in which Owen saved Charlotte Church from a tentacle monster, and they seemed to be keeping their word at the time. But Ianto's story has convinced Jack that he made a mistake. Jack thus visits the Perfection's club, but once there, he finds himself swept up in the emotion and music of the dance floor, and is unable to resist when Brendan and Jon seduce him and lead him upstairs. They explain that they made the machine to enhance their natural powers, but it draws energy from the beliefs of their followers -- and because it's been separated from them, their own need for energy has been increasing. Brendan and Jon spend the day shagging Jack's brains out, and then push his body into the wall of their flat, which is made out of the flesh of their other followers. Their victims have merged into a mass of inchoate screaming flesh, from which Brendan and Jon are drawing the energy they need to survive. They claim that they'll put everything right once they get the device back, but Jack isn't convinced. However, he's now melted into the wall and can't escape.

The energy field is growing more powerful as it drains the life out of Cardiff, and there's still no sign of Jack. Ianto calibrates a hand-held detector to sniff out Jack's unique 51st-century pheromones, and she and Gwen trace it to the Perfection's nightclub. The bouncer politely but firmly tells Gwen that they have their quota of fag hags, and because of the energy field, he's too dazed to defend himself when she breaks his nose. Gwen and Ianto enter the club to find the dance floor packed with entranced young men, and when they head upstairs to investigate the management, they find that the flat above the club is made of living flesh; limbs are sticking out of every surface and disembodied mouths are screaming for help.

Gwen and Ianto find Jack embedded in the floor of the bedroom, and he warns them that the energy the Perfection are drawing out of their followers is reaching critical mass. Brendan and Jon then arrive and immediately conclude that only agents from Torchwood could have made it past the club's psychic defences. Gwen and Ianto try to stall them, but they pick Gwen up and throw her into the wall. Ianto panics and runs outside to regroup, and once free of the Perfection's influence, she grabs the device and asks it what to do. Speaking in Jack's voice, the device tells her that it ran away with the Kieltys because it was bored of perfection, and explains how to put things right. Ianto thus returns to the Perfection's bedroom and gives them a chance to stop what they're doing, but they refuse, and reveal that they've decided to use the device to become Earth's new gods after all. Ianto thus reveals that the device will be able to put everything right if it drains all of the energy out of Brendan and Jon. Before they can stop Ianto, she gives the device permission to do so.

Everything that the device can return to normal, it does. The meat in the walls is separated back into individuals, although at least one ends up with a missing finger. Ianto gives them all retcon, telling them that it's tabs of E. Brendan and Jon are reduced to elderly husks, and Ianto gives them so much retcon that they'll never remember they used to be shining young gods. Ianto also sets up Patrick on a blind date with Emma, who has forgotten the events of the past week; no longer looking for perfection, she thus finds the good-enough Patrick to be a perfect match. Everybody from Lucky Debbie's hen party has survived the ferry disaster, and the Perfection's club is now back to the tatty little dive it used to be before they tried to make it perfect. Ianto and Jack take the device to the Bay, where it speaks to Jack in the voice of the man he admires most; however, instead of asking it for anything, he asks the device what it wants. Surprised, the device admits that it can never share in the perfection it creates for others, and that it just wants to rest. Jack gives it what it wants by tossing it into the Bay. Ianto will return to normal tomorrow, which gives her and Jack one night to explore what it's like with Ianto as a woman...