The book opens up with Percy being chased by 2 gorgons who are trying to kill him. He doesn't remember anything and ends up defeating the gorgons.
Percy, Frank, and Hazel compete in their camp's games and end up winning. At that moment, Mars, the god of war, shows up and tells everyone that Frank is his son. He also sends the 3 on a quest to Alaska.
In Alaska, the trio is faced against a titan who they must defeat. The 3 are very nervous and Frank has to melt the chains that are trapping Death.
Exposition of Next book
The trio yanks the titan to Canada and kill him. They summon Arion and they zoom back to Camp Jupiter
After the battle at Camp Jupiter, the trio are greeted by the Argo II which is being sailed by the demigods from Camp Half-Blood
The Journey continues as the 7 set sail for the ancient land to defeat Gaia in the next book.