The very awesome MI-5 Margaret, last seen getting her Slitheen ass blown off in "World War Three," turns out to have teleported at the last second and spent the last six months becoming Mayor of Cardiff. The Doctor, Rose, and Captain Jack TARDIS into town in order to refuel off the energy of the closed Rift from "The Unquiet Dead," meeting up with Mickey and impressing upon him that they are now bad-asses and a very special club for special people. The four of them figure out Margaret's still around and track her down; Mickey sucks some more. Margaret explains her plan to blow up Cardiff with a Bad As Designed nuclear plant, releasing enough energy that she can literally surf the wave away from Earth, and the Doctor notices the Bad Wolf issue for the first time. The crew takes her back to the TARDIS, planning to drop her off on her home planet once they've finished refueling -- which she explains will lead to her torture and execution. Mickey and Rose have an obnoxious and unending conversation about what a jerk Rose has been to him, and what a jerk he is for being cool with it, and are generally worthless for yet another episode in a row. Meanwhile, the Doctor takes Margaret on a date -- a last meal of sorts -- and avoids her numerous murder attempts with a hilarious Ã©lan. Less hilarious are the things Margaret and the Doctor have in common: mass murder, sneakiness, quick reflexes, and the desperate need for a second chance. Her pleas for clemency fall on mostly deaf but quite large ears, but when stuff starts going down with the Rift, everybody runs back to the TARDIS, and Margaret twirls her moustache anew and holds Rose hostage. The Doctor introduces Margaret to the TARDIS, something lovely happens, and Margaret is reduced to an egg. As the gang returns her home for a fresh start, Rose wonders if it's possible to start over again so cleanly with Mickey -- and whether she wants to. It's also possible, though seemingly unlikely, that she also realizes she's kind of a dick. This episode features hella nods to continuity both within this season and throughout the legacy, is touching and funny, and leads directly to the two-part finale, starting with "Bad Wolf" two weeks from now. Friggin' SciFi.
Six months ago, in London, several high-ranking British politicians, including the Prime Minister, were skinned and used as disguises by members of the mercenary Slitheen clan from Raxacoricofallapatorious. They faked an alien invasion in order to concentrate the world's UFO experts, and then killed almost all of them to keep their true goal -- destruction of the Earth so they could sell off the remains -- a secret. Mickey and the Doctor fired a few missiles on 10 Downing Street, and brought it down around the Slitheen, presumably killing them.
About 130 years ago, in Cardiff, Wales, a group of hungry spirits called the Gelth -- dispossessed by the Time War, which destroyed their world -- attempted to gain access, by way of an interdimensional Rift, to our world, where they hoped to inhabit the bodies of the dead. In their haste and greed, they threatened to turn all the world into zombies for their use. A young psychic woman laid down her life to close the Rift and stop their invasion, but it would seem to have left a scar.
Now, we're back in Cardiff, at the Wales Millennium Centre -- a performing arts complex that opened in November 2004. It was basically built because Wales always gets the shit end and can't help but push back sometimes. The top level's bar and lounge has windows that are letters; at night, the words light up, and we'll be seeing them a lot, throughout the episode. It's a double inscription written by the Welsh poet Gwyneth Lewis: "Creu Gwir fel gwydr o ffwrnais awen -- In these stones, horizons sing." In the literature, you find that Wales is second only to Cornwall in terms of strange doorways into other places. Thanks to the Gelth, the stones beneath their feet in Cardiff sing with the literal horizons of new worlds. Lots of charming and hopeful double-language signs and things in Wales; lots of insistence that a speaking population smaller than that of metropolitan Houston constitutes a living language, and not an archaic beauty. Don't call Welsh a dead language, by any definition linguistic or otherwise, unless you'd like to redefine "pedantry" in a pound or two of email. Mark my words. But it is a lovely language, and a lovely inscription. The first bit means, "Creating truth like glass from a furnace of inspiration." In other words: what the Doctor's been doing since the first time we met him.