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

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.
Defeat a vicious and bloodthirsty roman emperor the most vicious of three very vicious and bloodthirsty roman emperors.
Is that all. No, I’ve to do everything without any of my godly powers. Wonderful. Looks like I’ll be needing all the help I can get. From new friends and old