The prologue opens with a "formidable glass-and-steel structure" (Prologue.1), which is known to normal people as "a building."
It's a condo in Manhattan called the Metropole, and something weird is happening on the top floor, and not just the fact that someone can actually afford to live there.
A young warlock named Elias draws a pentagram on the floor to summon a demon named Agramon. There's another man there asking him to do this. Oh, this will end well.
Agramon appears inside the pentagram and taunts the young warlock. "Foolish boy," (Prologue.20) he hisses.
The demon manages to escape the protective ring of the pentagram and attacks and kills Elias. The man does nothing besides watch.
The man tells Agramon that he needs the boy's blood, and that he's the master of the demon now.
He holds up the Mortal Cup, which can control demons.
Agramon says, "I am at your service, my Lord…?" (Prologue.30)