Chasing a weevil through the streets of Cardiff, Captain Jack (John Barrowman) passes a restaurant where Gwen (Eva Myles) and her boyfriend Rhys (Kai Owen) are having dinner. She wants to follow Jack and Rhys orders her to stay, but she leaves with Jack. They see the weevil being captured by a team of strangers and taken away in a van. Toshiko (Naoko Mori) tracks the van to a deserted warehouse. She and Jack go there to investigate, and they find the body of a man mauled by a weevil. The dead man’s phone rings and when Jack answers it, he is told to drop the case. Owen (Burn Gorman) is sent to check out the owner of the warehouse. He meets with property agent Mark Lynch (Alex Hassell). Gwen ends her relationship with Owen, who is still distraught about the departure of Diane Holmes. Gwen tells Rhys about the affair but gives him a Torchwood memory pill so he will forget about it afterwards. Jack and Ianto (Gareth David-Lloyd) follow reports of weevil-style injuries and question a victim in the hospital. He refuses to talk because he is afraid of being killed.

Owen goes undercover while Jack and the others put a tracker on their captive weevil and let it loose, hoping it will be picked up. After getting into a fight in a bar, Owen and Mark Lynch become friendly. Mark wants to tell Owen what happens to the captured weevils. They are used in a fight-club, pitted against human volunteers. Each one puts down a thousand pounds and the one who lives longest wins it all. Mark goads Owen into a fight, but once the weevil lights into him, he changes his mind. Torchwood storms in and pulls him out before the weevil kills him. Mark goes into the cage to show he has no fear. Back at the Hub, Owen intimidates the captive weevils.

The episode was written by Noel Clarke, who played companion Mickey Smith, Rose’s boyfriend, in the 2005-6 series of Doctor Who. Obviously, it was inspired by the movie Fight Club.