The Last Prince of Atlantis Chronicles, Book II - Battle For The Crown, #2

Murder, betrayal, and heartbreak are not what Allen had in mind when he began his epic journey to become King of Atlantis.  His life changes instantly after one of his classmates is murdered right before his eyes at a Halloween high school dance. In response, Allen is forced to kill Drogan's brother, sparking his mortal enemy's rage and retaliation. Amid this fatal crisis, Allen and Athena break up, and Jake and Francisco's boyhood friendship is close to disintegrating.
As dangers escalate, this unlikely team must resolve jealousy, betrayal, and old-fashioned high school drama as they struggle to reunite in time to battle Drogan and the Gargoyles. All are in pursuit of the powerful King's Crown. Whoever finds the Crown will rule Atlantis - and the world.