Doctor: Christopher Eccleston (Ninth Doctor)
Companions: Billie Piper (Rose Tyler)
John Barrowman (Jack Harkness)
Richard Wilson – Dr Constantine
Florence Hoath – Nancy
Luke Perry – Timothy Lloyd
Albert Valentine – Jamie (The Child)
Cheryl Fergison – Mrs Lloyd
Damian Samuels – Mr Lloyd
Robert Hands – Algy
Joseph Tremain – Jim
Jordan Murphy – Ernie
Martin Hodgson – Jenkins
Vilma Hollingbery – Mrs Harcourt
Noah Johnson – Voice of the Empty Child
Dian Perry – Computer voice
Directed by James Hawes
Written by Steven Moffat
Script editor Elwen Rowlands
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 1.10
Series Series 1
Length 2nd of 2-part story, 45 minutes
Originally broadcast 28 May 2005
Continuing from the cliffhanger of "The Empty Child", the Doctor, Rose, and Jack are cornered in the hospital by the "empty children", patients who all have gas masks fused to their faces. The Doctor uses the ruse of an angry parent, loudly telling the patients to go to their rooms. It works, and the patients retreat to their beds. The tactic also works on young Jamie, the index case of the "epidemic", who retreats from his older sister Nancy. The trio go to the hospital room in which Jamie was first taken, where the Doctor realises that the child is still learning what it can do and soon will be too powerful to stop. Suddenly realising that he had just sent the child "to its room" which happens to be the room that they're standing in, the Doctor turns around and finds Jamie standing in the doorway.
Escaping from Jamie and the other patients, the three end up trapped in a room. Jack teleports back to his ship and plays music over the radio to prevent Jamie from using the radio to track the Doctor and Rose. Challenged by Rose to dance while they wait, the Doctor accepts but is interrupted when they are teleported to Jack's Chula ship. The Doctor uses the ship's nanogenes to heal a wound while Jack explains that he went renegade from the Time Agency after they stole two years of his memories. Meanwhile, Nancy returns to the railyard to tell the other children they are not safe while they are with her, because it is her that Jamie is trying to get to. She then tells them she is heading to the bomb site, but before she can reach it she's captured by soldiers. Despite her pleas, she is shackled and left with an infected guard who grows a gas mask on his face.
The Doctor, Rose, and Jack arrive at the bomb site and realise that the contagion is now airborne as the soldiers begin to transform. They free Nancy, who saved herself by singing a lullaby to the transformed soldier, putting him to sleep. The Doctor investigates the bomb, which is the cylinder he was chasing at the beginning of the last episode. He determines it is the empty shell of a Chula medical transport. Realising that the ship also contained nanogenes, the Doctor deduces that the transformations are caused by nanogenes who, never having seen a human before used Jamie's dead body in a gas mask as a template for all humans. Because the Chula were a warrior race and the vessel was a battlefield ambulance, the nanogenes have given the transformed beings enhanced abilities.
As they attempt to open the cylinder, they wind up triggering an alarm that calls all of the transformed humans to defend it. The altered people from the hospital arrive at the railway station. The Doctor reasons that since Jamie was the template, it is his mind that drives them hence their collective obsession with finding a mother. A distraught Nancy claims that the situation is all her fault before the Doctor realises that she's not his sister—she is actually his mother. Jamie heads through the gate and approaches Nancy, still asking if she is his mother. The Doctor pushes Nancy to tell Jamie the truth, which she does while hugging him. The nanogene cloud gathers around the two, and are able to identify Nancy's DNA as being that of Jamie's parent. The nanogenes properly revive, and heal Jamie. The Doctor gathers all of the nanogenes up, and sends them out with the correct template to repair all of the transformed people.
Meanwhile, a German bomb falls onto the site, but Jack uses his ship to capture it and hauls it out into space. Then the Doctor sets the medical transport to explode once everyone is safely far from it, thus destroying the technology and matching the historical records of an explosion at the site. After celebrating that "everybody lives", the Doctor and Rose head back to the TARDIS. Aboard his ship, Jack discovers that he cannot jettison the bomb or abandon his ship. Resigned to dying, he fixes himself a drink before hearing music and seeing the TARDIS parked at the back of the ship. He quickly joins Rose and the Doctor, and the three put on music and dance together as the TARDIS takes them off the ship.