Book excerpt: Sister Fidelma-an Eognacht princess and sister to the king of Cashel, a religieuse of the Celtic Church and an advocate of the Brehornn court-is one of the most interesting and compelling figures in contemporary mystery fiction. In this collection of short mysteries, Tremayne fills in many of the background details of Fidelma and seventh-century Ireland not found in the novels, and weaves his always-beguiling mix of history and mystery.