The Doctors embark on their greatest adventure in this 50th anniversary special. In 2013, something terrible is awakening in London's National Gallery; in 1562, a murderous plot is afoot in Elizabethan England; and somewhere in space an ancient battle reaches its devastating conclusion. All of reality is at stake as the Doctor's own dangerous past comes back to haunt him.

With Cybermen on the streets of London, old friends unite against old enemies and the Doctor takes to the air in a startling new role. As the Doctor faces his greatest challenge, sacrifices must be made before the day is won.

When Osgood is kidnapped by a rogue gang of Zygons, the Doctor, Clara and Unit must scatter across the world in a bid to set her free. But will they reach her in time, and can they stop an uprising before it is too late?

With UNIT neutralised, only the Doctor stands in the way of the Zygons.