Thunder God by Paul Watkins. About a young Norseman who gets abducted and sold off to an Eastern Emperor to be part of his "Varangian Guard", which consists mainly of Norsemen. Then, he escapes with his Celt friend to go back home to Altvik and be the priest. He was hit by lightning as a young boy and has psychic powers. It is good so far. 3/4 of the way through.