«Tokyo» by Mo Hayder

Student Grey Hutchins comes to Tokyo seeking answers to what happened during the notorious Nanking Massacre in which, in one city, the Imperial Japanese Army killed up to 300,000 civilians. Only one man can help her, a survivor of the Massacre, and now a visiting professor at the prestigious university of Todai in Tokyo; a man who is rumoured to possess documentary evidence of Nanking. But first Grey must gain his trust.