When the goddess Artemis disappears while hunting a rare, ancient monster, a group of her followers joins Percy and his friends in an attempt to find and rescue her before the winter solstice, when her influence is needed to sway the Olympian Council regarding the war with the Titans.

While protecting egotistical transfer student Orion, Artemis makes a mistake that later provides her with the chance that she has both hoped for and dreaded, to prove her courage to herself and others at Mount Olympus Academy.