Cardiff Cop Gwen Cooper (Eve Myles), on her first day with the rogue alien-hunters of Torchwood, is interrupted on a date with her boyfriend Rhys Williams (Kai Owen) by a meteor strike outside of the city. The army secures the area and Torchwood is called in. Owen Harper (Burn Gorman) taunts Gwen as the new girl and she throws a chisel at him, which strikes the meteor and cracks it open. A purple gas escapes and possesses a young woman, Carys Fletcher (Sara Lloyd Gregory). In a nightclub afterwards, she seduces a man and, during sex in the bathroom, he dissolves into dust, his life energy passing into her.
Torchwood learns of this and understands what has happened. They find out where Carys lives and arrive before she can seduce the postman. Owen traps her with a portable prison cell, which he is not supposed to remove from the Torchwood Hub. Carys is put in a holding cell. As she is being tested, Gwen is overcome by pheromones and the urge to kiss her. The condition is slowly killing Carys. She seduces Owen—apparently, not too difficult—and she escapes. Captain Jack (John Barrowman) tries to apprehend her, but she gets hold of the Doctor’s severed hand, which has a great deal of power, and gets away.
Toshiko (Naoko Mori) believes Carys will be after her ex-boyfriend. They arrive at his house to find him already dead. They learn she is a temp at a fertility clinic and race there to find many of its clients dead. Cornering her before she dies, Jack kisses her, passing on some of his limitless lifeforce. Gwen offers her body as a host to save her, but before the mist can enter her body, Jack throws the portable prison cell at it. The gas, unable to survive long on Earth, dies out. Gwen kisses Jack in thanks. Carys, alive, is united with her father (Brendan Charleson). As the team returns to Torchwood, Jack warns Gwen not to let the job consume her and tells her to go home and spend some time with her boyfriend.
Series creator, Russell T. Davies, said the Torchwood team is there for the aliens, science, technology, and mythology, but Gwen is there for the people, shown in the fact that it was she who really cared about Carys. On the wall of the Hub is a picture of Craig-y-Nos Castle, where Queen Victoria founded the Torchwood Institute. Sara Lloyd Gregory, who plays Carys, was Garth David-Lloyd’s (Ianto Jones) girlfriend. When Jack picks up the Doctor’s severed hand, the Doctor Who theme is played.