Roots: The Matrix. The Cold War (opposing power blocs). 1984. There are references to Barbarella, Elvis Presley, Harry Houdini, and A Christmas Carol.
Continuity: Skale is inhabited by humanoids who are have two hearts and are apparently otherwise physiologically similar to the Doctor. The planet is divided into Parallels (equivalent to countries), all of which are hostile to each other. There are at least 67 Parallels. The Northern Waters is a sea on Skale that borders Parallel 59. Great City is the capital of Parallel 59. Skale's society is built on flesh-tech. The Project was established thirty years ago to protect Parallel 59 from attack from Haltiel: it involved launching undesirables into space in capsules, where they are stored on space stations called Bastions orbiting in a network strategically placed around the planet. The inhabitants of the capsules are psychically linked together in a utopian virtual reality called Mechta, which they believe is actually a real, physical colony, unaware of their true location and situation. The psychic network forms an early warning system: it surrounds the planet and, if breached, causes the nearby capsules, with their prisoners inside, to explode. The rulers of Parallel 59 alone know the safe path through the barrier. It is implied that there are dogs [or equivalent] on Skale.
Haltiel is a neighbouring planet to Skale. Skalen probes have suggested a high-gravity world with a noxious atmosphere and have detected life-signs. The Haltiel Presence responds to the threat of the network by seizing control of it to trap the people of Skale inside it, preventing them from leaving their planet. They use the capsules to bomb Skale, with Parallel 6's Great City and its two million inhabitants the first victims. Parallel 90 is the first Parallel to launch missiles into space into retaliation, thus starting a war with Haltiel. The resulting war lasts three days, during which the Haltien Presence destroys virtually every city on Skale and wipes out most of the population: it withdraws once the capsules have all been destroyed. The survivors of Skale, from every Parallel, gradually start to talk to one another as the first step towards rebuilding.
To conserve life support for Compassion, the Doctor shuts down his cardiovascular system whilst in the lifepod. He and Compassion are stripped naked when they arrive on Skale. He uses his respiratory bypass system to feign death as part of an escape attempt (see Pyramids of Mars); he dislikes doing it, because as he gets older he's less likely to be able to snap out of it.
Since being Remembered by the TARDIS (Interference) Fitz has lost track of his age. His mind has started to work differently: he can now do crosswords and anagrams with ease. He becomes trapped in a capsule on Bastion 634 and thus spends some time "living" in Mechta, unaware, like everyone else in the capsules, of where he really is. Whilst in Mechta, he has a sexual (albeit virtual) relationship with Anya. He adopts a Mechtan accent during his stay. Sam used to try and interest him in counselling.
Compassion has been getting increasingly bad headaches for several weeks. When the body scanner in Parallel 59 tries to scan her, it explodes. She dons a guard's uniform whilst escaping. Her earpiece allows her to interface with the damaged network.
Skale is listed in the TARDIS databanks, but there seem to be few details about it.
Links: Fitz has a slight tan that he obtained on Drebnar and recalls Alura (Frontier Worlds). He recalls being brainwashed in China (Revolution Man) and visiting San Francisco (Unnatural History) and Antarctica (The Taking of Planet 5). Compassion mentions Kode (Interference). The Doctor recalls being in a morgue in San Francisco (The TV Movie). He refers to Daleks.
The Bottom Line: "Their world's not real, it's all meaningless." Dear god, this is dull. An alien planet that might as well be Earth, a collection of uninteresting characters, and a tedious, predictable plot that becomes interminable as soon as the twist appears add to an overlong mess with few redeeming features.