Percy the Overlander

Two months following the epic climax in Rick Riordan's The Blood of Olympas, Percy Jackson finds himself trapped in a mystery following his neighbor's heart attack and the disappearance of the man's son. He soon learns that he must go to a place beneath New York City called the "Underland", and when a mysterious visitor urges him to do otherwise, Percy is only encouraged. Set in the subterrainian world of Suzane Collin's The Underland Chronicles, this is one fan fiction crossover you don't want to miss!