Onyx, Nico di Angelo and Will’s child, is asleep and someone, a camper who has some kind of resentment toward them, sneaks in and places a ward in their room that is specially meant to drain them of their powers—and only them—both sunlight and shadows. The camper figured out the weaknesses of both and had been designing it for months to take down Onyx, and Nico and Will don’t notice it until morning when Onyx doesn’t wake up—because it is not designed for sunlight or shadow on their own, but both of them together in one being, so the ward is undetectable by both of their powers.