Doctor: Christopher Eccleston (Ninth Doctor)
Companion: Billie Piper (Rose Tyler)
Camille Coduri – Jackie Tyler
Noel Clarke – Mickey Smith
Penelope Wilton – Harriet Jones
Annette Badland – Margaret Blaine
Rupert Vansittart – General Asquith
Morgan Hopkins – Sergeant Price
Andrew Marr – Himself
David Verrey – Joseph Green
Steve Speirs – Strickland
Jack Tarlton – Tom Hitchingson
Lachele Carl – Trinity Wells
Corey Doabe – Spray Painter
Elizabeth Fost, Paul Kasey, Alan Ruscoe – Slitheen
Directed by Keith Boak
Written by Russell T Davies
Script editor Elwen Rowlands
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 1.5
Series Series 1
Length 42 minutes
Originally broadcast 23 April 2005
Following from the cliffhanger in "Aliens of London", the Doctor survives an electrical pulse from the Slitheen while Mickey Smith is able to push aside the impostor police inspector advancing on Jackie Tyler. The Doctor attempts to get the police, but by the time he has returned the Slitheen have gotten back into their suits. The Doctor escapes to the upper floors of 10 Downing Street and reunites with Rose and Harriet in the Cabinet Rooms. Just before sealing off the rooms, the Doctor confronts the Slitheen and learns that they are a family rather than a race. The Slitheen tell him that they are not invading Earth but raiding it for some commercial purpose.
Although the Slitheen have blocked all communications to the Cabinet Rooms, Rose's altered mobile phone allows her to make contact with Mickey and Jackie. The Doctor gives Mickey instructions on how to log into the UNIT website on his computer, and uses the information to determine that the Slitheen ship is presently in the North Sea transmitting a signal that the Doctor attempts to decode.
Green and the other Slitheen declare a matter of national security and request that the UN release the activation codes to launch a nuclear strike against a fictitious mothership supposedly hanging over London. The Doctor realises that the Slitheen actually plan to fire the weapons against other countries in order to start World War III. The Slitheen plan to sell the Earth's radioactive remains as a fuel source, which they have already begun advertising through the signal Mickey has decoded. The Doctor helps Mickey to hack into the controls of a Royal Navy submarine and fire a missile at 10 Downing Street. The Slitheen are caught in the explosion when the missile hits but the Doctor, Rose, and Harriet all survive. The press dismisses the events as a hoax.
Afterwards, Jackie invites the Doctor for dinner but he declines. The Doctor gives Mickey a CD to upload to the internet that will remove all mentions of the Doctor from the web. He also privately offers Mickey the chance to come travel with him, but Mickey admits that he's too scared and wouldn't be able to handle it. He asks the Doctor not to tell Rose about his concerns. Rose arrives with a full backpack and asks the Doctor if Mickey can come along, and the Doctor covers for Mickey by saying that he doesn't want him in the TARDIS.