Back on land, Ares has Hades’s helm. Ares reveals his plan to use Percy to start a war among the gods. The backpack he gave Percy is the lightning bolt’s sheath disguised. Like Riptide, the bolt would return to it, but Ares rigged it so the bolt would only come back once Percy was in the Underworld. Percy asks why Ares didn’t just keep the bolt, and Ares pauses “as if he were listening to another voice, deep inside his head” (323). Percy realizes the thing in the pit—whatever it is—used Ares, too. Percy battles Ares and tricks him into the ocean to deliver a massive blow. Something powerful stops Ares from killing Percy. Ares curses Percy to fail in battle and disappears.

The Furies arrive, having seen the entire confrontation. Percy returns Hades’s helm to them and orders them to tell Hades “to call off the war” (331). The Furies agree and fly away.

Percy, Annabeth, and Grover fly to New York, where Percy goes up to Mount Olympus by himself. After riding the Empire State Building elevator to the 600th floor, Percy finds a shining city of mansions atop a snow-capped mountain.