Percy Jackson and the Titan's Curse by Rick Riordan
It's not every day you find yourself in combat with a half-lion, half-human. But when you're the son of a Greek God, it happens. And now my friend Annabeth is missing, a Goddess is in chains and only five half-blood heroes can join the quest to defeat the doomsday monster.
Oh and guess what. The Oracle has predicted that not all of us will survive . . . The Greek Gods are alive and kicking