Doctor Who: The Ninth Doctor Adventures: Cloud Eight (4.04)

The Doctor and Rose travel to the 47th century, Earth's 'Second Dark Age', but when they arrive in the floating box city of High High Wycombe, it's more like a paradise. The residents live an existence of endless leisure, and at night sleep a blissful, dreamless sleep.

But cracks soon begin to show on its perfect, polished surface, and something terrible is brewing in the mind of teenage Elsa - something ancient and hungry - something that sounds like a nightmare.