In the episode, the alien time traveller the Tenth Doctor (David Tennant) climbs down a deep pit in which the Beast (Gabriel Woolf) is kept prisoner.
At the same time, the Doctor's travelling companion Rose Tyler (Billie Piper) and a human expedition team try to escape the planet after the Beast possesses the Ood on the base.
The Tenth Doctor and science officer Ida investigate a pit under a recently opened trap door deep in the planet Krop Tor.
Rose takes Zach's bolt gun and shoots out the rocket's front window, unhooking Toby's safety harness to jettison him into space.
It was re-released as part of the Complete Series 2 box set on 20 November 2006 with a commentary by James Strong, Mike Jones and Ranny Jhutti.
While he found some "scripting misfires" like the easy recovery of the TARDIS, he described the story as "action-packed, ambitious, emotionally draining and, thankfully, still willfully different to every other SF show out there.
He found it a disappointing conclusion which spent too much time getting the Doctor to the monster, only for him to confront it by "ranting and raving rather embarrassingly at a roaring CGI effect."
He also criticised the Doctor's concentration on saving Rose without mentioning the other characters, and noted that a few previously unseen crew members appeared and that "entire plot threads also go nowhere".
Still, he praised the acting of the guest cast, the music, and the effects, concluding that the two-parter was "a qualified success that offers solid character, brilliant visual design and some thought-provoking moments damaged only by poor plotting and some glaring missed opportunities".