There are different parallel universes and the crew of the Argo II gets to travel those worlds. Worlds like, what if Percy had turned to the titans? What if the children of the underworld had met in the 30s? What if Percy had ran away from Gabe as a child? What if Mortals still believed in the Greek gods? Nico/Percy slash Nicercy

Percy Jackson had gleaned a couple of things from the return of Nico di Angelo in his life: One, everything is better when you're drunk. Two: cigarettes taste bad but could be worse. Three: he might possibly be the teeniest-tiniest bit unequivocally gay.