Theo Paxstone and the Dragon of Adyron by James Turner

My name is Theo, and I've become a squire for Sir Bentham, a brave, crippled knight in the realm. Surprisingly, a gigantic dragon attacked the local festival, killed many brave knights, and kidnapped the princess. Why would a dragon take the princess instead of eating her? Someone must rescue her, so we're now using the steam mech I created from junk parts since Sir Bentham's damaged mech was destroyed by scavengers. Sir Drake, my childhood hero, is also searching for the princess, although Sir Bentham and his other squire, Riley, think he's a fraud. The dragon's strange behavior makes its motivations puzzling, but Sir Bentham is determined to slay it. I'm committed to helping him, although Riley makes the adventure more challenging. I can't figure out why Riley resents me so much.

I always enjoy a good underdog story, and Theo escaping the futility of existing with a greedy junkyard boss fits that description. His special talents for mechs and building things aren't superpowers, but they make him an unassuming hero. The most interesting part of the book is the relationship between Theo and Riley. They're very competitive in gaining Sir Bentham's favor, and Riley especially tries to take advantage of situations. Theo can't figure out the problem until he discovers Riley's secret. Sir Drake is another interesting character, although there are numerous hints along the way that he's not an honorable man. In contrast, Sir Bentham is an extremely honest and noble knight, but he can't physically handle the skills of a warrior. He's lost his legs, but his knowledge is invaluable. The plot boils down to rescuing the princess, but it's clear something's going on with the dragon. In the end, Theo and Riley unlock the mystery of its behavior and use that information to make a plan. The book contains plenty of action and adventure, so it can be enjoyed by most middle-grade readers. I highly recommend you give it a shot.