Atonement of Blood - Peter Tremayne

Winter, 670 AD. King Colgú has invited the leading nobles and chieftains of his kingdom to a feast day. The gathering is interrupted by a religieux claiming that he has an important message for the King. Suddenly, the man, shouting 'Remember Liamuin!' stabs King Colgú. The assassin is slain but Colgú is on the verge of death.