Book excerpt: At the end of his life, the Twelfth Doctor faced his darkest hour: losing beloved companions Bill and Nardole in an impossible stand-off against the Cybermen, and losing Missy to herself, not long after. Mortally wounded in battle, he could see no reason to go on. He was willing to die a final death. But a surprise, time-twisting encounter with his oldest self, the first Doctor, led him to recover his desire to go on – to start again. It’s time for change. For regeneration. And the Doctor has a few things to say to the Doctor that is to come. For in his warren of memories and the many lives past lies the key to a brilliant future…