An “ancient” pyramid appears overnight. Every clock in the world begins counting down to the Earth's destruction. Three opposing armies lie ready to annihilate each other. An alien race stands ready to offer humanity a deal that could save them, but also enslave them. It's a terrifying race against time to save the world. Will the Doctor be forced to accept their help?

• Sydney Newman
• Donald Wilson
• C. E. Webber

• Gerard Horan
• John Barrowman
• Mark Bonnar