In the mid-sixth century, one hundred years after St. Patrick brought Christianity to Ireland, most of the Irish Kings were Christian – at least in name. But Díarmait mac Cerbaill, in his attempt to consolidate his position as High King, had recourse to an older magic. In about 560 A.D., he held the last "Feast of Tara" – the old Pagan sacred wedding of the King with the Goddess of Sovereignty. And at the subsequent battle of Cul Dreimne, the Chronicle of Ireland reports that Fráechán mac Tenusán cast the "druidical fence" over Díarmait's army. In the event, Díarmait lost that battle due to "the prayers of Colum Cille" (Saint Columba).

But who was Fráechán mac Tenusán, and how did he come to be practicing Druid magic for Díarmait? "The King's Druid" is his story.