One hundred years ago, the universe's greatest library was sealed off, leaving only one warning: "Count the shadows". But now, the shadows are moving again. As Russell T Davies's Bafta Award-winning time-travelling drama continues, the Doctor and Donna must uncover the terrible truth behind the Nodes and the horrifying Data Ghost, to find the library's secret.

David Tennant plays the Doctor and Catherine Tate plays his companion Donna Noble, with guest stars Alex Kingston, Colin Salmon and Steve Pemberton.