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.