The Collegium Chronicles, book 2: IntriguesMercedes Lackey2010

Magpie has slaved in the gem mines of Valdemar for as long as he can remember. Overworked and underfed, he has nowhere else to go, until a stranger and two huge white horses force their way into the quarry, looking for him. An eternal outcast, Mags is stunned when he is chosen to be trained as a Herald at the newly founded Collegium in Valdemar’s capital city, Haven. Loyal, noble and just, Heralds are called upon to deliver messages, gather information and dispense justice on behalf of the King. Thrust into the centre of a legend in the making, Mags discovers talents he never knew he had and friendships he never thought possible. But when discord spreads through the capital, he learns that life in the court can be just as treacherous as the mines he left behind.