Doctor: David Tennant (Tenth Doctor)
Companion: Billie Piper (Rose Tyler)
Camille Coduri – Jackie Tyler
Noel Clarke – Mickey Smith
Shaun Dingwall – Pete Tyler
Andrew Hayden-Smith – Jake Simmonds
Tracy-Ann Oberman – Yvonne Hartman
Raji James – Dr. Rajesh Singh
Paul Kasey – Cyber Leader
Nicholas Briggs – Dalek and Cyberman voices
Catherine Tate – The Bride
Directed by Graeme Harper
Written by Russell T Davies
Script editor Helen Raynor
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Series Series 2
Length 2nd of 2-part story, 45 minutes
Originally broadcast 8 July 2006
Continuing the events of "Army of Ghosts", the episode opens with Dr. Singh, Mickey Smith, and Rose Tyler trapped in a sealed room within the Torchwood Institute. Four Daleks, accompanied by a device known as the "Genesis Ark", have emerged from the Void ship. A black Dalek called Dalek Sec extracts information about Earth from Dr. Singh, killing him in the process. Dalek Sec discovers that a separate invasion is in progress, and sends Dalek Thay to investigate. The Cybermen who took control of Torchwood also detect the Dalek technology and confront them, offering an alliance. The Daleks decline and kill two Cybermen, causing the Cyber Leader to declare war on the Daleks.
Ms. Hartman and Jackie are taken by the Cybermen for conversion, but the Cyber Leader orders the Doctor held aside because he has valuable information about the Daleks. The Cyber Leader is destroyed by a strike team led by Jake Simmonds, who have traveled from their universe in pursuit of the Cybermen. Ms. Hartman is converted, but Jackie escapes into a stairwell. Jake uses a device around his neck to take the Doctor to the parallel universe and their version of Torchwood. The Doctor meets with the alternate universe Pete Tyler, who tells him that after he left the Cybermen were sealed in their factories while humanity decided what to do with them. In the meantime, the Cybermen vanished and the breach began causing unprecedented global warming on the parallel Earth, which the Doctor theorises is the start of the process that will lead to both planets falling into the Void. Pete demands the Doctor seal the breach before his Earth is destroyed.
Meanwhile, Rose deduces that she and Mickey were kept alive because their touch can activate the Genesis Ark. Dalek Sec explains that they cannot open the Ark because it is stolen Time Lord technology. He demands that Rose open it, but she refuses and mocks the Daleks until the Doctor arrives. The Doctor realises that these Daleks are the enigmatic Cult of Skaro, and uses his sonic screwdriver to allow the Cybermen into the sphere chamber. As the Cybermen attack the Daleks, Mickey accidentally activates the Ark while escaping. The Daleks battle the Cybermen and Dalek Sec takes the Ark outside. The Doctor and his companions flee into the tower. Along the way, Pete saves Jackie from the Cybermen and the two embrace. The Doctor then takes everyone to the control room where they witness the Genesis Ark open and millions of Daleks that were imprisoned during the Time War pour out and begin engaging the Cybermen firing on them from below, though humanity is caught in the crossfire and many are killed while running for cover.
The Doctor explains that crossing the Void causes a traveller to become saturated in Void material. If he opens the breach and reverses it, anything saturated in Void material will be pulled in. Everyone except Jackie has crossed the breach and is thus vulnerable to being trapped in the Void, so the Doctor sends them all to the parallel universe. Rose decides she would rather be with the Doctor than her family and jumps back to help him. The Cybermen attempt to stop the Doctor but are repelled by a converted Ms. Hartman, who has resisted the effects of her conversion and at least partially retains her sense of self. The Doctor and Rose open the breach and hang on to magnetic clamps as the Cybermen and Daleks are pulled into the void. The Cult of Skaro use an emergency temporal shift to escape. Rose's lever slips, and in resetting it she loses her grip and plunges toward the Void. At the last second, Pete reappears and grabs her, and together they transport back to the parallel universe. The breach closes, leaving a devastated Rose trapped in the parallel universe. The devices used to travel between the two worlds have also stopped working. The Doctor presses his ear against the wall, as a tearful Rose does the same in the other universe, as if trying to listen for each other.
Some time later, Rose has a dream where she hears the Doctor's voice calling her. The Tylers follow the voice to a remote bay in Norway called Bad Wolf Bay, where a holographic image of the Doctor appears. He tells Rose he is using the energy of a supernova to transmit to her via one last small breach between universes. Rose breaks down in tears and tells the Doctor that she loves him, and he responds, "Quite right, too, and, I suppose, if this is my last chance to say it: Rose Tyler—"; before the Doctor can finish his reply, the breach seals and the Doctor's image disappears. In the TARDIS, tears run down the Doctor's cheeks as he slowly regains his composure and sets a course. As he gets back to piloting the TARDIS, he notices a mysterious woman in a wedding dress standing in the TARDIS console room. With the Doctor shocked and confused, the mysterious bride angrily demands to know where she is, leading to the events of "The Runaway Bride".