View from the mirror, book 1 : A shadow on the glass
Ian Irvine1998

Karan is forced to steal an ancient relic in payment for a debt, but is not told it is the Mirror of Aachan - a deceitful thing that remembers everything it sees. Llian is expelled from his college for uncovering a perilous mystery. Thrown together by fate, they are hunted across a world at war.