The fact was simple, sort of. Nico di Angelo, son of Hades, had to go on a quest. To Tartarus, the most vile place in the universe. But why? Well, Nico had a series of nightmares, in which he was begged by someone to come and help him. Nico came to the conclusion that the person in question was Bob the Titan, formerly Iapetus, Titan of the West, who had sacrificed himself so Percy and Annabeth could escape through the Doors of Death. You happen to be in a polyamorous relationship with Nico and Will Solace, son of Apollo, and you and Will aren't gonna let Nico go alone. Will: "Nico, I'm not going to just stay back here and let you go off and get killed or driven insane!"