The Thief Lord
Prosper and Bo are orphans. Their aunt Esther wants to adopt Bo, but not Prosper, so the boys run away to Venice to escape being separated. There they join a gang of other orphaned children, led by a boy who calls himself The Thief Lord. Things get interesting when a strange man commissions the kids to steal a wooden wing for him, and Esther hires a detective to track down her nephews.
At first glance this story is quite simplistic. But wait until you get about a hundred pages in, and you have a very complex book in your hands. Nothing is really as it seems here. Unfortunately, near the end the story takes a completely unexpected turn toward fantasy, which while interesting and clever, is also confusing without any foreshadowing. Other than that, though, The Thief Lord is worth reading.