The Maul and the Pear Tree: The Ratcliffe Highway Murders 1811, by P. D. James and T. A. Critchley. New York: The Mysterious Press. 234 pp. $17.95. First published in Britain in 1971, this fascinating study of the murders of seven people in Regency London should appeal to mystery and history buffs alike. In 1811, the members of two households near the London Docks were murdered. P. D. James, the renowned mystery writer, and T. A. Critchley, a police historian and Miss James's former colleague in the Police Department of the British Home Office, provide a detailed examination of the events and the evidence based on contemporary records. They point out the carelessness of the investigators, conclude that the main suspect, who supposedly died by his own hand, was in fact murdered, and identify him.