The hidden oracle / Rick Riordan.

Enhanced descriptions from Syndetics:

Favorite Greek and Roman demigods return in a new five-book adventure quest with a fresh twist: they're helping Apollo regain his immortal status.
"A clash of mythic intrigues and centuries of pop culture to thrill die-hard and new fans alike."-- Kirkus Reviews #1 New York Times best-selling series Rick Riordan is considered the "storyteller of the gods" because of his five #1 New York Times bestselling series based on mythology A continuation of the Percy Jackson saga, but it also stands alone A new take on Greek and Roman mythology from the point of view of a fallen god Brings back beloved demigod characters from the Percy Jackson and Heroes of Olympus series Introduces new demigods Villains are based on Roman emperors Features a diverse cast with people from all kinds of backgrounds and lifestyles Perfect for middle schoolers but can be enjoyed by older readers, too How do you punish an immortal?

By making him human.

After angering his father Zeus, the god Apollo is cast down from Olympus. Weak and disoriented, he lands in New York City as a regular teenage boy. Now, without his godly powers, the four-thousand-year-old deity must learn to survive in the modern world until he can somehow find a way to regain Zeus's favor.

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.