The Tyrant’s Tomb by Rick Riordan

You will get to the Tiber alive. You will start to Jive. I am Apollo. I will remember. The former God Apollo, cast out by his father, Zeus, is having a pretty rough time of it. Well, for one thing, he’s called Lester. But being an awkward mortal teenager is the least of his worries. Though he and his friends (some of them) have emerged from the Burning Maze, rescued the Oracle and lived to fight another day, they can’t escape the tragedy that has befallen them, or the terrible trials still to face. So, with heavy heart, Apollo (OK, Lester) and Meg have a triumvirate still to defeat, oracles to rescue, and prophecies to decipher, so that the world may be saved, and Lester may ascend into the heavens to become Apollo once again. But, right now, Caligula is sailing to San Francisco to deal with Camp Jupiter personally, and they have to get their first. Or risk its destruction.