Daemonic by Stephen Laws

Mr Draegerman requests the pleasure of your company. If you come with us, this ten thousand is yours. You get another fifty thousand when you get there.

Jack Draegerman loves deals.

He made his first fortune directing popular horror movies. Then he became even more successful in the fields of engineering and architecture.

No one has seen Jack Draegerman for twenty years. He lives in a huge fortress he designed and built himself. Known as The Rock, its interior is a crazy structure of labyrinthine, descending corridors. With no way out.

But now, a band of uniformed henchmen are approaching a selection of unconnected people on Draegerman's behalf. He wants hem to visit him, and he's prepared to pay for the privilege.

Because Jack Draegerman has made contact with a Daemonic force. A Daemonic force who also loves a deal.