Heroes of Olympus

5 books set

Size - 19*13 cm

520 - 590 pages per book

Age 11 and up

The Heroes of Olympus is a pentalogy of fantasy adventure novels written by American author Rick Riordan.  The novels detail a conflict between Greek demigods, Roman demigods, and Gaea (Roman name Terra) also known as Mother Earth. In the fourth book of the series, there is also a semi-large fight against Tartarus, which, in Greek mythology, was the darkest and deepest point of the underworld. The series is a sequel to Percy Jackson & The Olympians, which detailed the life of modern-day Greek demigods. The sequel to this series, and the 3rd series in the trilogy is The Trials of Apollo.  Riordan introduces Roman mythology in his sequel series as well as several new characters. 

From Book 1:

Jason has a problem. He doesn't remember anything before waking up on a school bus holding hands with a girl. Apparently she's his girlfriend Piper, his best friend is a kid named Leo, and they're all students in the Wilderness School, a boarding school for "bad kids." What he did to end up here, Jason has no idea—except that everything seems very wrong.