The False Prince by Jennifer A. Nielsen. He is one of four orphans that a nobleman named Conner buys. Conner pits the boys against each other in a series of deadly games. He plans to use the winner to impersonate a prince who has been missing for years. The winning boy will ultimately become a puppet king, but the losers are lose ends that will need eliminating.
This book had a gripping combination of action and intrigue. There are plots within plots and all sorts of devious twists. Sage is smart and snarky and that makes a great narrating voice. I can't say too much more without giving it away, but this one is definitely worth reading.