Sim, spoilers:
Harry is told that the target is Hades in his first briefing from Nicodemus, 5% of the way through the book (can't give you a page number as it's an ebook).
Aqui está a cotação atual:
"Who?" I asked him. "Whose vault are you knocking over?" "An ancient being of tremendous power," he replied in his roughened voice, his smile widening. "You may know him as Hades, the Lord of the Underworld."