Gwen has been thinking about whether there really is an afterlife, and when an alien trader from Murgatroyd gives Torchwood a strange device, she decides to take him at his word and speak into it. There are people she wants to talk to, whether they can hear her or not...

24-year-old Steven Ballard considers himself the life of the party, and only hangs out with his work colleague Darren Sowersby because Darren makes him look good. After a night out on the town, Steve and Darren share a cab back to Splott, but they're both quite drunk and Steve, bored with the constant routine and irritated with Darren for trying to strike up a conversation with the taxi driver, cruelly tells him that nobody really takes an interest in him. In retrospect he decides that he was being a bit harsh, but this is only after he falls asleep in the cab and wakes up to find himself abandoned on the streets of Cardiff with no one else around. It takes him fifteen minutes to realise that there is literally nobody else around at all; Steve is literally alone in the world, and for him, that's a personal Hell.

Two days later, a call from PC Andy interrupts Gwen's shopping trip with Rhys; the skeletal remains of a 70-year-old man have been found on Queen Street and positively identified as Steven Ballard, who was 24 years old when he disappeared two days earlier. Based on the CCTV footage of the taxi ride, the police have arrested Darren Sowersby, who was apparently the last person to see him alive, but Darren insists that he passed out in the taxi and can't remember what happened next. Gwen sends the CCTV footage to Tosh for analysis and questions Darren, who admits that he's afraid he may have done something to Steve after all; when Steve lashed out at him in the taxi, for just a moment Darren was so upset that he wished Steve were dead. He insists that Steve was just having a bad day and meant nothing by it, but what if his wish came true?

Tosh and Ianto watch the CCTV footage and see the interior of the taxi go black just after Darren and Steve's argument; when it returns to normal, Darren is alone in the back seat. Ianto contacts Jack and Owen, who have been out hunting a Weevil; they return to the Hub with their captive, while Gwen brings Darren back to the Hub and locks him up in the Vaults. Tosh determines from the footage that alien energy was present in the taxi, and Ianto and Jack both recognise it as huon energy; Torchwood One was trying to synthesise huon particles before its destruction, and it can be used to teleport people vast distances instantaneously. The question is how Darren got hold of this ancient, dangerous energy -- or at least that's the question until Ianto points out that nobody thanked him for bringing coffee to the meeting. Most serial killers don't know their victims, and people who work quietly in the background tend to be taken for granted -- just like the person who must have been driving the taxi.

Elsewhere, a young woman named Jade Russell chats with her friend Steph over her mobile, complaining about the receptionist who kept her so late that she had to hail a cab, and gossiping about her inferior friends. The cab driver, judging her guilty of the sin of pride, quietly sings "ring-a-rosies" as he opens a box of matches, and tells her to go to Hell. Jade tries to flee from the thing chasing her and ducks into a club called the Priory simply because its door is open -- but once she's inside, she finds that the door has vanished, and that everyone she's ever known is in the club, pointing at her and whispering, humiliating her and judging her. Within 43 days, she's run out of food; 212 days later, she's torn off her ears so she won't have to listen; but she's still praying for death 4,306 days later...

Jack confronts Darren, playing bad cop until he's satisfied that the terrified Darren is indeed innocent. Tosh picks up a police report about a body being found at the Priory nightclub, and Jack, Owen and Gwen set off to investigate. Tosh tries to enhance the taxi's number plate from the camera footage while Ianto chats with Darren, trying to find out more about Steve. Darren explains that Steve stood up for him at work; he had a kind side despite his brash exterior, just as Darren is more than the shy, timid geek he appears to be. But perhaps the taxi driver judged Steve based on that one random outburst in the cab.

While Owen examines Jade Russell's remains, Gwen interviews Skip Jameson, the Priory barman, who found the body when he opened up the club. Jack is proud of his team as he watches them, although he knows that pride is a sin. Owen determines that the woman died of old age even though she apparently tore her own ears off. He takes the body back to the Hub for further study, but Tosh then calls Jack and Gwen to report that the taxi belongs to Patrick Jefferson of Grangetown, and that he's just used his credit card at a petrol station on Newport Road. Jack and Gwen set off to hunt him down, and Jack cockily tells Skip to give Gwen his phone number; maybe Jack will give him a call when this is all over. Back at the Hub, Darren is astonished by Tosh and Ianto's confidence that this will all be over once Jack catches the taxi driver.

Gwen calls Rhys to tell him that she'll be late for dinner, which develops into an argument when he reminds her that she already skipped out on their shopping trip. Jack suggests that Gwen needs to take a break from Torchwood, but before he can pursue the matter, she spots Jefferson's taxi, and sees that he has a passenger in the back seat. As the SUV begins to pursue the taxi, it speeds up to get away from them -- and Gwen gets a call from PC Andy, who asks if she's following him. It had started to rain at the end of his shift, and, already irritated that Torchwood had taken over another of his cases, he'd flagged down a taxi to get home quickly. Gwen warns Andy that the driver is the killer they're looking for, but when Andy tries to place him under arrest, Jefferson drives off the road into a patch of scrubland. Andy is knocked senseless when the car leaves the road, but Gwen and Jack catch up to the taxi and emerge from the SUV, guns drawn. Jefferson -- a nondescript, middle-aged man -- judges Jack guilty of the sin of arrogance, pulls a matchbox out of his pocket, and begins to sing "ring-a-rosies." A black shadow emerges from the matchbox and envelops Jack, who vanishes, screaming. Laughing, Jefferson tells Gwen and Andy that he's an angel, and that he's sent Jack to Hell.

Jack emerges from the darkness to find himself in the flat once owned by Alex Hopkins, the Torchwood leader who murdered his entire team on the eve of the millennium. On the television, AMNN anchor Trinity Wells and Suzie Costello mock him for his fear of aging, and claim that he's died and gone to Hell. Trinity interviews Rhys, who claims that Gwen left him because Jack made her feel that Rhys wasn't good enough for her; Captain John Hart, who has taken over Torchwood and forced Ianto into an abusive relationship with him; and Owen and Tosh, who have finally found love now that Jack isn't standing in their way. Alex appears in the flat and tells Jack that this really is Hell, which seems to be confirmed when the TV starts to play Bryan Adams' Everything I Do. Rather than listen to it again, Jack shoots himself in the head, falls back into the shadows, and emerges back on the wasteland, safe and well.

Jefferson's mind is broken by Jack's safe return from Hell, and he offers no resistance when Jack and Gwen take him back to the Hub. There, Ianto asks Jack about their relationship, and Jack inadvertently hurts his feelings by making a joke about it. Jack is confident that the matter has been resolved, until Ianto tells him that someone delivered grey roses while he was away; the choice of flowers -- grey, rose, and rose petals -- is meant to remind him of those he's lost, and the card with the bouquet first reads "You've got the wrong man" and then changes to "You've got them all wrong." Disturbed, Jack interrogates Jefferson, who is singing "ring-a-rosies" and who tells Jack that "we all fall down." Jack questions Jefferson about the roses, and when Jefferson claims to have no idea what Jack's talking about, Jack loses his temper and breaks Jefferson's arm. He then breaks Jefferson's spirit by telling him of all the sins that he and his friends have committed, and when Jefferson continues to insist that he didn't send the roses to Jack, Jack kicks him in the face.

Jack returns to his office to ask Gwen if Tosh has finished analysing the card, but Gwen claims that Jack never asked her to. Jack finds the card in his pocket, and it now reads, "You've got everything wrong." Gwen wonders if Jack has been affected by the time he spent in Hell, but Jack insists that he's fine; however, he is starting to wonder whether they could use the matches, Jefferson's little lucifers, to fight their enemies. Gwen warns him that they're not here to judge people, but the voices in Jack's head remind him that Gwen cheated on Rhys, and, upset by her strident moralising, he pulls a revolver out of his desk and shoots her dead to shut her up. Horrified by what he's done, he tries to convince himself that the lucifers made him do it. The Hub suddenly seems haunted by the ghosts of everyone he's ever let down, and when he looks for Ianto, he finds Ianto making out with Darren in the boardroom. Ianto cruelly tells Jack that he only got close to him to punish him for killing Lisa, and reminds him that the one man he admires most in the world abandoned him as well. Unable to take another betrayal, Jack opens the matchbox and sends Ianto to Hell. As he huddles in the boardroom, staring at Ianto's skeletal remains, he receives a call from St Helen's Hospital, telling him that Owen and Tosh have died in a car crash. But Jack was already expecting this, because he knows he's in Hell.

Back in the real world, Gwen has put Jefferson in the Vaults. She calls Rhys, tells him what's happened, and asks him just to be there for her when she comes home. Owen has conducted autopsies on Jefferson's other victims, and has determined that they died of old age after a lifetime in Hell -- but Jack can't die, which means that he'll be there for eternity. Gwen tries to keep everyone's spirits up, and tells Owen to keep Tosh company while she analyses the huon energy and tries to reverse its effect. Gwen and Ianto question Jefferson, hoping to find out where he acquired the matches. They find Darren hammering at the cell door, infuriated by Jefferson's calm certainty that he was doing God's work when he killed Darren's best friend; however, while Darren acknowledges that he wants Jefferson to go to Hell, that wouldn't bring Steve back.

Darren returns to the main Hub while Gwen and Ianto question Jefferson, trying to keep themselves calm as he insists that he's been doing God's work; at the same time, Tosh is learning about Jefferson based on computer records. Jefferson is the illegitimate son of a prostitute, and he grew up in Bluebell Field, a children's home in Swansea that was shut down after allegations of child abuse going back decades. Jefferson used to sing "ring-a-rosies" to himself when he was sinned against, and he always tried to believe that God would one day come to punish the sinners and keep him safe. When he received the matchbox in the post, it came with a note telling him that he could use it to punish those who had sinned. He used it on his dog when it bit him, and then on the drunken vagrants he saw surrounding him on the streets, and then on all others he judged guilty of sin. But Ianto reminds Jefferson that God told them to forgive sinners, and he returns to the Hub, convinced that if Jefferson can punish, then Ianto can forgive.

All of Torchwood One's records on huon energy were lost during the Battle of Canary Wharf, and Tosh must start analysing its composition from scratch based on the CCTV footage of Steven Ballard's disappearance. If they open the matchbox in the Hub and send someone after Jack, she might be able to lock onto them and bring them both back, but she's by no means certain. Ianto rushes into the Hub and demands the matchbox, and when Gwen follows him in, she inadvertently distracts Owen just long enough for Ianto to grab the matchbox and open it. Tosh desperately starts up her program, but the shadow consumes Ianto before she's ready.

In Hell, three years have passed, and the creatures from Jack's childhood have destroyed all life on Earth except for him. He's alone in the Hub, slowly going mad, until an angel that looks like a man in a suit appears in a blaze of light, takes his hands and forgives him. Jack and Ianto reappear back in the real Hub, where the relieved Tosh tells them that the system locked onto the huon energy, found them and brought them back. Darren stands back as the others celebrate Jack's rescue, and decides not to point out that Tosh's program was only 96% complete when Jack and Ianto returned.

The team turn Jefferson over to PC Andy and plant evidence at his home, ensuring that he will be punished as a serial killer without their having to bring up the existence of his matchbox in court. Jack theorises that amoral scientists sent the matchbox to Jefferson as an experiment that just kept running after the fall of Torchwood One. Darren returns to the real world with a greater appreciation for life, and Jack decides not to give him retcon, instead trusting Darren to keep silent about what he's seen. The team then relaxes in the Crown and Thistle, where Jack tries to laugh off his experience, insisting that he was just transported to a different dimension and not the mythological Hell. He gives Gwen two tickets to Paris, telling her to take a proper vacation with Rhys and promising that Torchwood will still be here when she returns. As she goes, the rest of the team return to their work. But Jefferson feels no remorse for what he's done, and remains convinced that God has other angels out there, punishing the sinners. In London, a married man named Johnny pulls a woman at the White Rabbit pub while his wife's away, and as they head back to his place in a taxi, he arrogantly demands that the driver allow him to smoke on the way. The driver offers to give him a match...

Gwen has been thinking about these events since Tosh and Owen died, wondering if Jack really did go to Hell and if that means that there's an afterlife. If there is, then maybe the device she's speaking into really works, and maybe she can tell her friends that they're missed. If there is a life after death, then she hopes her friends are in a good place.