In "Erin's Blood Royal: The Gaelic Noble Dynasties of Ireland," Peter Beresford Ellis dons his historian's cap. He's better known as Peter Tremayne, writer of the beloved "Sister Fidelma" novels, but moonlights as a preeminent historian of Celtic history. This new edition traces the early history of Ireland through the stories of 19 dynastic families. ($29.95, 384 pages, Palgrave)