Among the mad

On Christmas Eve 1931, Maisie Dobbs is on her way to meet a client when she watches a man take his own life on a crowded London street. The next day, a letter reaches the prime minister's office. It threatens mass death unless demands are met, and it names Maisie.

Detective Chief Superintendent Robert MacFarlane of Scotland Yard's Special Branch questions her and clears her. He then brings her into his own domain as a special adviser. Her task is to help find a man who has shown he has both the knowledge and the will to kill thousands of people.

Away from the case, her assistant Billy Beale faces trouble at home. His wife has never recovered from the death of their young daughter, and her grief is deepening into depression.

The book is a historical mystery with a thriller's urgency, set in London in the early 1930s. The pace is driven by the hunt for a single dangerous man. The mood is dark, and it darkens further as the investigation leads Maisie toward a despair she last met as a nurse on the wards of shell-shocked soldiers.