On the edge of darkness

I have just read Barbara Erskine's book "On the Edge of Darkness". A really great read. Seemed to drag a little in the middle, but maybe that was because I wanted to know what happens in the end and couldn't read quickly enough. It has a slightly Science Fiction flavour - something I have not read much of TO DATE but I think I will look into more books of that kind.
It's about a young boy who stumbles into the six century, gets involved with a ..... you had better read it for yourself. K