The Torchwood group are in full flight as they race through the busy evening streets of Cardiff. From the Hub, Toshiko is using the sensors to track something of alien origin that’s moving fast in the direction of the Castle. She’s been unable to make any visual contact on the city’s CCTV system, but the gap between the group and their target is getting smaller. Jack warns them to avoid any heroics as they don’t know what they’re up against yet. Toshiko identifies their target as a young man wearing a hoodie, but as Gwen catches up with the teenager, she gets separated from the others by a descending security grille at the shopping arcade. Just outside the railway station, she grabs the man’s jacket, but he slips free and gets away. Toshiko congratulates her on her success and it becomes clear that the target was not the teenager but something in his jacket. Gwen finds a strange alien device in the pocket and activates it. She finds herself having an out-of-body experience where she’s still in the same location, but everything around her is from a different time. She sees a young boy dressed in 1940s school uniform who appears to be lost. He has a suitcase and a name tag - Tom Erasmus Flanagan - and looks very much like a wartime evacuee. Things return to normal and when they others catch up with her, she tells them she’s just seen a ghost.
Back at the Hub, the group review the CCTV footage of Gwen snatching the teenager’s jacket and then a few seconds later she is joined by Jack and Owen. There’s no evidence on film of anything unusual happening. Gwen assures them she didn’t just see the little boy, she could actually feel what he was thinking. Owen theorises hallucinations or dementia, but Jack is more interested in examining the alien device for clues. Toshiko has lots of CCTV footage of the guy they were chasing, so tracking him down should be fairly easy, but when she offers to run a full computer check on the name written on the boy’s tag, Owen beats her to it by simply looking him up in the local telephone directory.
The next morning Gwen and Owen call at the address listed for Tom Erasmus Flanagan and are introduced to an elderly man. They claim to be police officers looking for eye witnesses to an incident at the train station last night, but both Mr Flanagan and his daughter say they were home watching television. Gwen sends Owen to help make a cup of tea while she talks alone to the old man. He tells her he’s lived here for 66 years after being evacuated in 1941. He arrived at the railway station, with just a suitcase and his name written on a tag attached to his school uniform, but there was a mix-up and he was left alone at the station. Eventually he was taken in by a lovely childless couple and after his parents were killed during the war, he stayed in Wales. Gwen realises he was the young boy she saw in her vision.
As she and Owen leave, Gwen receives a phone call from Rhys, who wonders whether she’ll be home tonight. She isn’t sure and Rhys becomes frustrated. He doesn’t mind the secrecy surrounding her new job, but the uncertainty is causing problems for their relationship. If she can’t commit to being home, he’ll make alternative plans and go out with his friends instead.
The young man carrying the alien device has been identified as Sean Harris, also known as Bernie. He’s 19 years old with a string of convictions for burglary, shoplifting, theft and credit card fraud. The device itself was made using advanced nano-technology, but they can’t seem to get it working now, so they decide to concentrate on questioning Bernie. The group split up and visit locations where he’s known to hang out. They begin by visiting his mother in an area east of the city centre called Splott, but she’s banished him from the house until he pays back the money he owes her. Various other contacts at the local shops, snooker hall and amusement arcades are equally unhelpful and the group eventually end up despondent and eating a take-away under a disused railway bridge. Jack decides their only course of action now is to analyse the device again in laboratory conditions and try to recreate the events of last night as far as possible.
As they pass through the tunnel, the device suddenly becomes active and Owen experiences a similar out-of-body experience. He’s still in the same place, but it’s now a stormy night. He sees a young girl crying after a confrontation with her boyfriend. Owen tries to communicate with her, then realises he isn’t really there. Her boyfriend, Eddie Morgan, arrives and calls out the girl’s name - Lizzie. She’s obviously terrified of him and tells him her friends warned her not to go with him. Owen can tell instantly that Eddie dominates Lizzie, yet she resists when he tries to force himself on her. Angered by her refusal, he strikes her and then pulls out a knife. Owen watches in terror as Eddie drags her to one side and attacks her. He finds himself back in the present, but is too shocked to tell the others much about what he’s just experienced.
Later, the group discuss what they know. Like Gwen, Owen didn’t just witness these events, he actually felt the emotions of the people even though they lived years ago. From his description, Jack deduces that the girl came from about 40-45 years earlier and Toshiko tracks down records of a murder victim named Lizzie Lewis who was raped and murdered in the tunnel on March 29th 1963. No one was brought to trial, but Owen remembers the name Ed Morgan and Toshiko gets to work. Meanwhile, Jack has established that the alien device is a quantum transducer that can convert one form of energy to another. In this case the device takes quantum energy from human emotion, amplifies it and converts it into something other people can actually sense. It’s a bit like déjŕ vu or the feeling there’s someone behind you when you walk into an empty room. Owen wants Toshiko to check for witness statements or coroner’s reports relating to the crime, but Jack reminds him that for a case to be reopened you need new evidence - and they can hardly present what they have to the police or in an open court. Jack insists their priority is to track down Bernie Harris and find out what he knows about the ghost machine, not to investigate a 40 year old murder.
Jack summons Gwen to the Torchwood firing range and decides it’s time she learnt how to use guns. Slowly at first, he takes her through the best techniques and by the end of the session she’s become proficient with a range of weapons. The hours have passed by and it’s time for her to go home. She asks Jack when he goes home and is surprised to learn that he actually lives in the Hub. He claims he doesn’t sleep and she wonders whether he ever gets lonely at night.
Gwen returns home but finds the place is empty. Rhys has left a message saying that he’s playing poker with his friends (and winning!) and has decided to stay overnight. Eventually the temptation to experiment again with the alien device becomes too much and she switches it on. She finds herself reliving the day when she told Rhys she’d become a fully trained police officer. She tries again and this time she sees herself fussing over Rhys as they prepared for her mother’s 60th birthday. Back in the present day, she realises how much she misses Rhys when they’re not together. At that moment, he returns home early because his friends ended up having an argument. He tells her he doesn’t mind her working all hours, just as long as she still wants to come home at the end. She promises him she does and they kiss.
Owen has also gone home, but he can’t get his experiences with Lizzie and Eddie out of his head. He spends the next few hours going through all the archive research material he’s collected, including police statements that show Edwin Morgan was brought in for questioning by the police about Lizzie’s murder but was released without charge. On a whim, Owen tries the telephone directory again and finds an entry for E Morgan at 46 Pryse Avenue, Cardiff.
The next morning, Owen visits the address using fake ID. An elderly man opens the door and Owen asks to come in to check reports of a gas leak. After establishing they’re alone in the house, Owen starts asking questions about how long Morgan has lived in the street and whether he remembers some of the old neighbours from years ago - in particular Mabel Lewis, whose daughter died in 1963. Morgan becomes very agitated and uncomfortable, especially when Owen starts describing Lizzie exactly as she was the night he killed her. Eventually Owen tells him he knows what happened under the bridge that night and the elderly man jumps up and demands he leave his house. Just before Owen is thrown out, Morgan mentions having told him before that he’ll get nothing from him.
As Owen returns to his car, he notices a young man in a hoodie sitting nearby - and he recognises him as Bernie Harris! The teenager sprints off and a lengthy chase ensues through the streets and the back gardens of the neighbourhood. Eventually he catches the youngster…and they end up in a nearby pub where they’re joined by the others. After Bernie explains that he got his nickname from when he burnt his neighbour’s shed down at the age of 12, Jack shows him the alien device and asks him where it came from. He claims that he and a friend were using a lock-up that belonged to an old man, which was filled with odds and ends, including some foreign coins and weird bits of rock. They thought the device might be worth something so they planned to sell it. Bernie warns them that the device makes you see strange things and he tells them about a young woman he saw putting her dead baby into the canal. He knew the woman, but she’s old now and when he tracked her down, she offered him money not to tell anyone. He also experienced the murder of Lizzie Lewis. The group have heard enough and prepare to leave, but Bernie calls them back and asks them if they want the other half of the device!
Back at Bernie’s flat, he gives them the other half and shows them the money and rock, which also turns out to be alien. It’s more driftwood, washing in through the rift. They realise Bernie must have split the device into two pieces and they wonder what it can do now that it’s whole again. The teenager tells Gwen that he only used the other half once and it terrified him. Instead of showing him the past, it showed him the moment he’s going to die - in the road just outside the estate. Most disturbing of all, in the image he was exactly the same age he is now, which means he’s going to die very soon.
Gwen catches up with the others in the road and is about to tell them what she’s just learned when she accidentally activates the complete device. Jack rushes to stop her, but it’s too late. During an out-of-body experience she sees another version of herself in the same road, but this version is covered in blood and is holding a knife. The future Gwen explains that Owen had the knife and wanted to kill someone, and that she couldn’t stop what happened. The present-day version of Gwen finds herself back on the road with her concerned friends around her. She views Owen with suspicion…
Back at the Hub, Gwen tells her story to Jack in private. She didn’t actually see Owen in her vision, but they know Bernie has already witnessed his own death and now she’s seen a vision in which she spoke about Owen having a knife at the same location, yet it was Gwen that was holding the knife. Jack theorises that this was just one of many possible futures. Whatever she and Bernie saw, it might never happen. She finds this a comfort and decides it’s worth telling Bernie the same.
Alone in his house, the elderly Ed Morgan is trying to summon up the courage to call a telephone number he’s written down on a piece of paper, but keeps changing his mind. Later, Bernie’s telephone rings and he answers it…
In a nearby bar, Toshiko tells Owen that she’s managed to track down Ed Morgan, and Owen admits that he also found him and even paid him a visit earlier in the day to frighten him. Toshiko has read his medical records and has discovered that Morgan is claustrophobic, paranoid and depressive, and has attempted suicide twice. He’s barely left his house in years. Owen mentions the fact that Morgan thought he was trying to blackmail him and said he’d told him before that he’ll get nothing from him. They realise someone else has already been trying to blackmail Morgan…
Gwen visits Bernie at his house and tries to reassure him that even though he’s seen a future vision of his death, that doesn’t mean it’s definitely going to happen, but the teenager is becoming increasingly nervous. Gwen’s phone rings and Jack tells her that Owen has confessed to visiting Morgan. It looks like he succeeded in frightening him, but because Bernie had already tried to blackmail Morgan first he’s likely to think the two men are working together. He tells her to stay with Bernie as he and Owen are on their way. Toshiko stays behind to monitor the CCTV in case Bernie tries to make a run for it. Toshiko discovers from Morgan’s medical records that he was admitted to hospital about fifteen years earlier after suffering paranoid delusions and violent fantasies. She then sees the elderly man on the CCTV, stumbling along the street in the direction of Bernie’s house. She warns Jack and they try to get there as quickly as they can.
Gwen confronts Bernie about his blackmailing scheme, but the teenager sees something through the window and leaves his house. Realising that may well be the moment Bernie dies, she rushes after him. She finds Morgan and Bernie confronting each other in the street. The old man has a knife and claims to have been waiting for years for someone to come after him. He’s always believed he could see his guilt in the faces of people when they looked at him. He tried to hide, but they always knew. Gwen tries to calm him down, but he becomes aggressive towards her. Bernie promises Morgan that he won’t say anything, but Morgan says he’s come here tonight to make sure.
Jack and Owen arrive and grab Morgan from behind. Owen manages to disarm the man, but then turns the knife on Morgan and holds it up to his face. He wants the old man to know what it’s like to feel the fear, just like he did himself when he synchronised with Lizzie. Gwen takes the knife away from Owen, relieved that they appear to have changed what she saw - but while Jack is distracted, Morgan deliberately steps forward and impales himself on the knife in her hands. He falls to the ground and although Owen tries to resuscitate him, it’s too late. Morgan is dead. Gwen goes into shock, swearing that she was too close and couldn’t stop what happened.
The group take Gwen back to the Hub and Toshiko assures her that Morgan wanted to die and would have found a way, no matter what they did. Owen knows he’s screwed up, but he didn’t kill the man even when he had the chance. Jack blames the alien device as the problem with looking into the future is that you can’t just sit back and watch, you have to try to change things. The device is too dangerous, so he gives it to Ianto to place in the secure archives. Gwen tells Jack that no matter what anyone else says, she feels responsible for killing Morgan and she’s still got his blood on her hands. It’s nearly dawn and the city will be awake soon. Jack points out that they’re surrounded by ghosts all the time, even though they can‘t see or feel them. There’s a million shadows of human emotion out there and they’ve got to learn to live with them.