An old lady is preparing to cross the street as a car pulls up. An alien, the Blowfish, stops and waves her by. Once she passes, he drives on. Torchwood drives by a few minutes later and asks if the Blowfish just went by. The old woman tells them and they leave, as she complains about Torchwood.
As the team continues in pursuit, Owen complains that Jack has disappeared. They spot the Blowfish up ahead and speed up. The chase runs through the streets of Cardiff and Owen leans out to open fire. He hits a tire and the Blowfish's car skids to a halt. The team moves in as they hear a gunshot from a nearby house. Running in, they discover the Blowfish has taken the daughter hostage and wounded the father. The Blowfish is wired on cocaine and boasts that Torchwood is useless without Jack. As he taunts them, a shot rings out and he goes down. Jack steps out and asks if they missed him.
Back at the Hub, the team goes to work without needing Jack. Gwen finally points out that he left without warning. Jack says that he found his Doctor, but he didn't get fixed or need to be, and he came back for them. As an alert goes off, the team responds, unaware of a flashing red pyramid device in the Blowfish corpse's pocket.
Atop a car park, a glowing field appears and a man steps out of it. He hears someone yelling and goes to investigate. The man finds a mugger attacking a victim. The newcomer casually tosses the mugger over the side of the building, and then tells the victim to forget he was ever there. The newcomer then goes to get a drink.
The man arrives at a nightclub and uses a wrist device to shut down the music. He tells everyone but the most attractive people to get out. The bouncers come by and the man draws two guns as everyone panics. The remaining people run for it.
Torchwood investigates the dead mugger and detects temporal energy on his neck. As they go back to the SUV, Jack's wrist unit bleeps. It never bleeps. Jack turns it on and an image of the newcomer appears, explaining that Jack has probably already traced him. He apologizes for the mess and tells Jack to follow the transmission for drinks. Jack tells them to stay behind and then leaves in the SUV. Tosh starts tracking him and Ianto hails a cab.
Jack arrives at the nightclub and finds the man, Captain John, drinking alone. The two men walk toward each other and start making out. John then slugs Jack, who slugs him back. The two fight, wrecking the bar. Meanwhile, the team heads for the bar and discusses the situation, complaining they don't know anything about Jack's background. They have to admit it's more fun when he's there.
Jack and John finally draw guns, banter, and stop to drink. John explains that the Time Agency has shut down and there's only seven Agents left. Jack tells him to leave his territory. John starts to snap back then fires toward the doors. The team comes in, armed, as Jack tells them everything is okay. He makes introductions and John explains that they were partners. Jack finally asks why he's there and John explains that he was working with a woman who got shot. She was working with three radiation bombs and they ended up in Cardiff via the rift. The radiation will break down the canisters and contaminate the city. Jack wonders why John is involved but he claims it's for benevolent reasons. He explains that he doesn't know where they are and figures that they can provide the local info. Jack warns him that once they've found the bombs, John has to leave.
The team goes back to base and takes John along. Jack has him give up his weapons and Gwen wonders why Jack let him in. Jack insists there might be a chance John is telling the truth and they can't risk disbelieving him. Gwen wants to know what the Time Agents are and Jack insists it's in the past. She wants to know why he deserted them and refuses to let it go. Jack explains that he saw the end of the world, and knew that he belonged with Torchwood. He takes Gwen's hand and notices she's wearing an engagement ring. Gwen explains that Rhys asked while he was away. She notes that no one else would have her and Jack congratulates her.
Tosh tracks three surges of temporal energy and they split up into three teams of two. Tosh and Owen go North, Ianto and Jack go west. Gwen takes John with her over Jack's objections. Privately, she tells Jack she's going to flirt with John and find out what he's really up to.
As the team searches, Gwen asks how John met the woman and he claims they were in love. John is reluctant to talk about how she died and who shot her. Rhys calls to tell her that he got the job and wonders if she'll be back before breakfast. She congratulates him and hangs up, only to discover that John has slipped away momentarily. He notes that it's probably wise not to be too trusting, particularly with her boss, and John says that it's best not to rely on Jack. They open another storage container and find one of the storage containers. John then kisses her, his lips dosed with paralyzing lip gloss. He warns her that she has two hours until her organs go into shutdown. As he leaves, he warns that Jack won't stay with her and that he and John shared something. As he goes, he tosses away Gwen's Blackberry.
Owen and Tosh search a warehouse and Owen explains that he figures he needs a proper woman now. He asks about her dating situation and she admits she has the same problem he does. Owen finds the cylinder but John arrives, knocks Tosh down, and threatens to shoot her unless Owen drops his gun. He's muted the comm systems so they can't call Jack. He takes their phones and then shoots Owen.
Jack and Ianto search an office building and Jack wonders how Ianto is doing. He suggests that when they're done, they go for dinner and a movie. Ianto is fine with that but wants to know why they're helping John. Jack says that John is part of his past and then wants him gone once they're done. They split up to search and Jack goes to the roof. Ianto hears the elevator arrive on his floor and goes to investigate. John gets the drop on him and takes his gun, and then tells him he has just enough time to save them. Ianto demands to know why he's doing it and John says it's about the money.
On the roof, Jack finds the third canister. John arrives and takes the canister, and then asks Jack to partner up with him again, out among the stars. Jack says he can't and insists he has a new life. Jack tosses the canister over the side and John shove him after it. Jack falls to his death.
Ianto tries to call Jack and the others without success. At the warehouse, Tosh tends to Owen's side wound. Ianto finds them first.
John goes down to the plaza and gets the third canister. He contemplates John's corpse and then takes his wrist strap.
Ianto, Tosh, and Owen search the storage containers and find her phone. The paralyzed Gwen can faintly hear it away. Tosh triangulates the location of Gwen's last call and they find her. They determine she's been poisoned and work to find the antidote.
At the Hub, John removes pieces from the three canisters and then complains to the Blowfish's corpse that he got himself noticed. John removes the pyramid and attached it to the mechanism from the canisters. Gwen and the others arrive, guns drawn, and Jack walks in. John is surprised to see him alive and Jack explains that he can't die. John wonders how it feels every time he has to drag himself back and says he pities Jack. They ask why he wants the canisters and John explains that the woman had stolen an Arcadian diamond and sent it through a personal rift storm to keep him from getting it. John turns it over and admits he killed the woman he was talking about.
The team takes the device and John explains it will give them the location of the diamond. A hologram of the woman appears, and explains that there's no diamond. The device opens to reveal a floating disk that attaches to John. The hologram explains that it's an explosive device intended to latch onto her killer's DNA, and will detonate in ten minutes. Jack warns that it will be a big explosion and John begs them for help. John wonders why and John grabs Gwen to take her as a hostage. He handcuffs her to him and swallows the key. Gwen suggests that Tosh uses the rift predictor programme so that she and John enter the rift, saving the city. John figure she's bluffing but Gwen warns she isn't. Tosh determines that the rift is still open atop the car park where John arrived. As they leave, Jack and Owen stay behind and start mixing blood samples from the team.
Gwen, Tosh, and Ianto head for the roof with 51 seconds to spare. The rift opens and Gwen drags John toward it. She tells Ianto to tell Jack something, but before she can finish, Jack and Owen arrive. They inject John with the blood sample but nothing happens. Owen explains they're trying to confuse the explosive. It detaches with seconds to spare and they throw it in the rift, which absorbs most of the blast and throws them back to the moment when John arrived. John reveals he kept the key in his mouth instead of swallowing it. He frees Gwen, who slugs him. Jack recovers his wrist strap and tells John to go now while he can still harness the residual rift energy. John gives him one last kiss but as he leaves, he tells Jack that he found Gray. John remembers holding a child's hand, but tells the team it's nothing.