Another great title from the Caudill 2015 nominee list!
The False Prince (part 1 of a trilogy) by Jennifer Nielsen is set in an alternate history middle ages. Four teenage orphans living in the realm of Carthya are picked up by a nobleman named Conner. Conner forces the boys into a brutal competition for the chance to impersonate the heir to the realm, long lost Prince Jaron. Political intrigue, unforeseen alliances, deadly combat and lies and truths all mix to make an exceptionally well written thriller full of surprises.
All three parts of the series are available in the LTC: The Runaway King and The Shadow Throne.