The war the gods have dreaded for years finally breaks open. Kronos, the Titan lord, has gathered an army and means to march on Mount Olympus, which sits hidden above the Empire State Building in the heart of New York. With the Olympians drawn away to fight a greater threat, the city's defense falls to a thin line of demigods, satyrs, and unlikely allies. Percy Jackson stands at the center of it all, shadowed by a prophecy that says a child of the eldest gods will make a choice on their sixteenth birthday that saves or destroys Olympus, and his birthday is days away. As his most dangerous summer unfolds, Percy makes a perilous bargain to gain an edge for the coming battle and rallies the demigods of Camp Half-Blood into a desperate stand across Manhattan. Old enemies, buried secrets, and the true meaning of the prophecy converge in a climactic siege that demands sacrifice from nearly everyone. This fifth and final volume pays off five books of building tension with its largest battles, its hardest losses, and its most emotional reckonings. Riordan brings the saga to a close that honors its themes of loyalty, family, and the fragile line between heroism and ruin, while keeping the warmth and wit that defined Percy from the start.