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."(艺术本来是弥补人生和自然的缺陷的，一切美的事物，都需要我们自己去发现和经营。)