The Silver Hand — Stephen R. Lawhead

Meldryn Mawr, lord of the Llwyddi, has been cruelly slain--and his son, the malevolent Prince MeldrQn, has claimed the vacant throne of Prydain. But only the bard Tegid Tathal has the power rightfully to confer kingship. And he chooses Llew, once called Lewis Gillies--a young Oxford student drawn by friendship and duty into the mystical, unstable realm. But with Llew's ascension dawns the Day of Strife--when civil war will threaten havoc in both the world and the Otherworld...and when courage, challenge, hope and sacrifice will help to mold a true sovereign.