The Crack Between Worlds (A PJO and KOTLC crossover)

Keefe is on the run in the forbidden cities when they find him. At first they seem like a vanisher and a hydrokinetic, but their eyes say otherwise. They aren't elves, and they certainly aren't humans.

Percy and Annabeth are enjoying a day in New York when they run into a possible demigod. They take him back to camp, and he passes through the border, but something is off about him.

When demigods meet elves, tensions build and forgotten enemies arise as century old secrets are unraveled. The two species must unite in order to save both their worlds, and everything is about to change.