The Doctor faces the end of his life as the Master's plans hurtle out of control. With the sound of drums growing louder, and an ancient trap closing around the Earth, the Doctor and Wilf must fight alone. But sacrifices must be made, and the deadly prophecy warns: "He will knock four times."

The Ood have given a warning to The Doctor. The Master is returning yet that is not the biggest threat. A darkness is coming which brings with it The End of Time.