The Burning Maze (The Trials of Apollo Book 3) by Rick Riordan

The third title in Rick Riordan's Trials of Apollo series - set in the world of Percy Jackson. I was a god, once, until I was cast out by my father, Zeus. Now I'm an awkward mortal teenager called Lester. My way out? A series of scary and dangerous trials, of course. For my third mission, I must: Journey through the Labyrinth to free an Oracle who only speaks in puzzles. Which sounds easy. Then, defeat the most vicious of three very vicious Roman Emperors. Is that all? No, I have to do everything without any of my godly powers. Wonderful. Looks like I'll need all the help I can get - from new friends, and old . . .