When the Doctor falls through a crack in time he finds himself in the Horizon Gallery. But it's no ordinary art gallery, because this one has the best view of the most impossible wonder of the universe — the Paradox. Tour parties are eager to see this stunning, hypnotic portion of sky that’s beyond description, and it's Penelope's job to stop people staring up at it for too long. For the Paradox's beauty drives people mad. The Doctor, Amy and Rory are about to discover that the Paradox also contains a giant and frightening creature with a taste for death...