Twelve-year-old Donny Taylor was rescued from certain death in a burning building. His savior, a mysterious girl named Angela Obscura, seems to be able to walk right out of the flames. Although she appears to be a teenager, Angela is actually an ancient dignitary from the underworld who needs the help of a mortal. And she's chosen Donny.

Hades, a bizarre, cavernous world that was once filled with pitchforks, fiery pits, and dismemberments, has recently become a kinder, gentler place where people can contemplate their transgressions rather than face eternal punishment. Now known as Sulfur, the underworld went through a period of reformation punctuated by a violent revolution that left the vicious old guard, the Merciless, defeated and imprisoned.

But it soon becomes apparent that the Merciless are plotting a comeback. If they succeed, they will reignite the long-extinguished Pits of Fire with a billion souls inside. And reformers like Angela and Donny will face Annihilation: the utter destruction of the consciousness and the soul, a nothingness more final than death itself.

With everything on the line and billions of souls to protect, Donny--a mortal and outsider--becomes the key to the underworld's salvation and the only one who can save Sulfur.