"The Satan Pit" is the ninth episode of the second season of the British science fiction television series Doctor Who. It is the second part of a two-part story, following "The Impossible Planet". With the TARDIS seemingly lost, Rose and the remaining humans are trapped on the base with the possessed Ood, while the planet floats helplessly towards a black hole. Meanwhile, the Doctor is trapped in the heart of the impossible planet where he encounters the Beast, a creature implied to be the Devil himself.

The episode was first broadcast on 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 door outside. 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 they are stronger as the Beast is alone, until the Beast has the lift cable snap, trapping Ida and the Doctor 10 miles underground.

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