Doctor: David Tennant (Tenth Doctor)
Companion: Billie Piper (Rose Tyler)
Danny Webb – John Maynard Jefferson
Shaun Parkes – Zachary Cross Flane
Claire Rushbrook – Ida Scott
Will Thorp – Toby Zed
Ronny Jhutti – Danny Bartock
Paul Kasey – The Ood
Gabriel Woolf – Voice of the Beast
Silas Carson – Voice of the Ood
Directed by James Strong
Written by Matt Jones
Script editor Simon Winstone
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 2.9
Series Series 2
Length 2nd of 2-part story, 45 minutes
Originally broadcast 10 June 2006
The episode opens where "The Impossible Planet" left off, with the Doctor and science officer Ida Scott investigating a strange door deep in the planet Krop Tor. Rose and three of the surviving members of the crew, Mr Jefferson, Danny and Toby, flee from the advancing Ood, who have all been possessed by the Beast and are killing people with their translators. The group initially believe Toby to be still possessed by the Beast, but Rose convinces them to change their minds by reminding them that they saw it leave his body and enter the Ood. The Doctor makes contact with the crew, revealing that nothing has exited the trapdoor that he and Ida are investigating. He offers to rappel down into the pit to further investigate, although he is actually lowered on a winch, but Captain Zach orders everyone to regroup so that he can execute "strategy nine". As the Doctor and Ida prepare to return to the base, the Beast communicates with the Doctor and the rest of the crew through the Ood and explains that he is the epitome of evil across all religions. The Beast tells them that he was sealed in the pit before the universe began and is seeking to escape. The Beast demoralises each member of the crew by playing on their fears and weaknesses, and says that Rose "will die in battle, so very soon". However the Doctor begins to reassure the crew that the Beast is using their fears against them, as well as the fact that they can use their advantage of numbers to defeat the Beast. The lift cable snaps shortly after, trapping Ida and the Doctor 10 miles underground, and briefly cutting off communications. This is done, as pointed out by Rose, to stop the Doctor from inspiring the crew to fight back, and defeat the Beast.
With Captain Zach cornered in the base control room by Ood, Rose and the rest of the crew decide to head to Ood habitation to incapacitate the Ood by turning off the telepathy that keeps the Ood functioning. They are forced to head through shafts designed for robots transporting resources, whilst Captain Zach uses the escape rocket's energy to have the air supply follow the crew through the shafts. However, the Ood enter the shafts and give chase. Mr Jefferson holds back to buy the others time with his machine-gun, and is unable to make it to the next section of the shafts in time. Knowing that Captain Zach cannot save him without sacrificing the air supply of the others, Mr Jefferson chooses to die by oxygen starvation, rather than suffer "death by Ood". Rose, Danny and Toby are then almost cornered by more Ood, but manage to escape the shafts and knock out the telepathy of the Ood to incapacitate them, although Toby is shown to be still unknowingly possessed by the Beast. Rose, Danny and Toby reunite with Captain Zach. The crew then knock out the unwilling Rose and take her with them to board the escape rocket and leave the planet.
Meanwhile, the Doctor and Ida use the lift cable to explore the pit, although the Doctor finds nothing but darkness far below. He then chooses to detach himself and fall, landing at the bottom thanks to an air cushion and finds that he can breathe. Finding cave paintings depicting the Beast's final battle and imprisonment, the Doctor discovers two jars on pedestals a few feet from each other as their light reveals the physical form of the Beast. The Doctor quickly deduces from the unintelligible grunts coming from the Beast that its consciousness has already escaped and that Krop Tor was designed as the perfect prison for the Beast: its jailers devised the jars as a failsafe, since their destruction would cause the planet to plunge into the black hole with the body of the Beast destroyed, and the mind killed in the process. Although the Doctor realises he must also sacrifice Rose and the others to destroy the Beast, he smashes the jars anyway on faith in his companion. As the planet falls out of orbit, the Doctor accepts his fate by mocking the Beast, before stumbling across his TARDIS while fleeing the collapsing cave.
On board the rocket, the collapse of the gravity field causes Toby to reveal the mind of the Beast is still possessing him as he taunts the others while breathing out fire. Rose takes Captain Zach's bolt gun and shoots out the rocket's front window, unhooking Toby's safety harness to jettison the possessed man into space towards the black hole. The cabin is sealed by automatic shields but the rocket still lacks the power to escape the gravity well. Suddenly their ride smooths out and the rocket turns away from the black hole. The Doctor contacts Captain Zach, telling him that he is towing the rocket to safety with the TARDIS. The Doctor asks for Rose and jokingly offers to trade Zach back Ida, whom he rescued from the planet caverns, for Rose. The Doctor reports he did not have time to go back and save the Ood, who were innocent victims of the Beast's possession. Once safe, the respective crews depart on their separate ways. As they return to Earth, Captain Zach reads off the list of personnel that died, including the Ood.