Two burglars break into a flat owned by a woman called Beth and her husband. There is a struggle and the burglars are suddenly terrified as a flash of light fills the room. Soon, Torchwood are on the scene investigating the fatal injuries sustained by the burglars.
Beth cannot remember events and is taken into custody by Torchwood, who suspect she is an alien. When they take her to a cell, she passes a Weevil and it cowers in her presence. Captain Jack decides to take drastic measures and subject Beth to a mind probe.
Despite no initial reaction, the probe eventually uncovers alien technology buried under the skin of her right forearm. It emerges that she is an alien ‘sleeper agent’, yet to be activated and oblivious to her real identity, having been given memory implants.
Around Cardiff, other sleeper agents are suddenly activated, with their right arms transforming into bayonet-like weapons. They all immediately kill someone close to them - a doting husband snaps his wife's neck, a paramedic walks away from a terminal patient and a young woman simply abandons her baby to let it roll into the road - and carry out a series of suicide bombings at key locations such as a telecommunications center taking out the Cardiff phone lines, killing the Leader of the City Council who is in charge of the city during emergencies, and taking out a military fuel pipeline, paving the way for their leader - the former husband - to head for an army base containing nuclear warheads.
Beth manages to escape and is found with her ailing husband at the hospital. She struggles to remain human but accidentally stabs her husband in his bed. Jack and Gwen manage to apprehend her and convince her to help them track the locations of the other sleeper agents.
Captain Jack manages to find the leading sleeper agent at an army base moments before the agent can detonate the nuclear weapons that are held within. Jack is stabbed in the process and the agent warns him that there are others of his kind on Earth before blowing himself up. Jack, Gwen and Beth barely escape from the explosion. Back at Torchwood, Beth tells Gwen she cannot live knowing that one day she will not be herself anymore. She uses the weapon in her arm to threaten Gwen, forcing the others to shoot and kill her. Beth uses her last piece of humanity to kill herself.
The episode ends with Gwen telling Jack that if more agents come, Torchwood is prepared against them.
John Barrowman – Captain Jack Harkness
Eve Myles – Gwen Cooper
Burn Gorman – Owen Harper
Naoko Mori – Toshiko Sato
Gareth David-Lloyd – Ianto Jones
Paul Kasey – Janet the Weevil
Nikki Amuka-Bird – Beth Halloran
Dyfed Potter – Mike Lyndon
Doug Rollins – David
Claire Cage – David's wife
Sean Carlson – Mr. Grainger
Victoria Pugh – Mrs. Grainger
Luke Rutherford – Burglar 1 (Leonard Bull)
Alex Harries – Burglar 2 (Gareth Hopkins)
Dominic Coleman – Police officer
William Hughes – Boy
Millie Philippart – Girl
Matthew Arwel – Pegram Driver
Derek Lea – Paramedic
Writer James Moran
Director Colin Teague
Script editor Brian Minchin
Producer Richard Stokes
Chris Chibnall (co-producer)
Executive producer(s) Russell T. Davies
Production code 2.2
Series Series 2
Length 50 mins
Originally broadcast 23 January 2008