The BBC have released the synopsis for episode twelve of the new series, The Pandorica Opens, read it below:

The Doctor's friends unite to send him a terrible warning; the Pandorica – which is said to contain the most feared being in all the cosmos – is opening, as the time travelling drama continues. But what's inside, and can the Doctor stop it?

The Pandorica Opens is written by Steven Moffat and stars Matt Smith as the Doctor and Karen Gillan as Amy Pond.