Just before Christmas in 1920, six people sat down to a meal at Morija, headquarters of the Paris Evangelical Missionary Society in Basutoland (Lesotho). All six were taken violently ill, and one of them died. They had been poisoned. The dead man was douard Jacottet, an eminent scholar and missionary. There was no trial and subsequently no one was ever convicted of the murder.Who killed Jacottet? Drawing on the great tradition of the "locked room"...