The Paradise War by Stephen R. Lawhead is still available for free. If you ever wanted to give this author a try, this is the perfect opportunity.
The Paradise War follows Lewis’s search for his missing roommate, Simon, which takes him through a door between worlds into the land of Albion. There he finds Simon–and a new life as Llew, warrior for Albion’s king. He fully intends to return with Simon to England. But Simon, now Siawn-Hy the champion, has grander plans–and a position of power that sets the two of them on opposite sides in a conflict of epic proportions.