The long-awaited prophecy surrounding Percy Jackson's sixteenth birthday unfolds as he leads an army of young demigods to stop Kronos in his advance on New York City, while the Olympians struggle to contain the rampaging monster, Typhon.

"The future has been saved, but at a cost: Fort Fitzgerald has been expelled from the Oppenheimer School, and some of Fort's friends have been lost in time. But time is the one thing Fort, Rachel, and Jia don't have, as they'll soon be facing one of the eternal Old Ones, the Timeless One, for the fate of the world. If they lose, the Old Ones will return, and humanity is doomed. If they win, the Old Ones will still return, and humanity is doomed. Because...

Destiny or desire? Where does your allegiance lie? I am told my union to the crowned prince will determine the fate of the kingdom, but it isn't my betrothed who haunts my dreams. It's the half-breed prince who stands at his side. He is darkness and sin, and when he whispers promises of wickedness in my ear, I crave a man who I can't have. Every thought I have is treasonous. The way my hands ache to touch him deceitful. Even my dreams make me a traitor...