The Trials Of Apollo: The Hidden Oracle

Now, without his godly powers, the 4,000-year-old deity must learn to survive in the modern world until he can somehow find a way to regain Zeus' favour. But Apollo has many enemies - gods, monsters and mortals who would love to see the former Olympian permanently destroyed. Apollo needs help, and he can think of only one place to go: an enclave of modern demigods known as Camp Half-Blood.