The Doctor sat alone and listened to the beat of his remaining heart. He had never got used to it. He never would. The single sound where a double should be. What was this new code hammering through his body? What did it mean? Mortal. No, he'd always known he could die. Not mortal. Damaged. Crippled. Through his shirt, his fingers sought the thick ridge of his scar. Human...

The Doctor's second heart was taken from his body — for his own good, he was told. Removed by his sometime ally, sometime rival, the mysterious time-traveller Sabbath. Now, as a new danger menaces reality, the Doctor finds himself working with Sabbath again. From a seance in Victorian London to a wild pursuit on Dartmoor, the Doctor and his companions work frantically to unravel the mystery of this latest threat to Time... Before Time itself unravels.