The Ninth Circle

The Ninth Circle is a bar type of place inside of Underworld Concourse which is in the Museum of History. Here, you can buy a "slave" that will follow you around helping you in combat and such. This slave is known as Charon, and you can purchase the contract for him by giving 2,000 (or 1,000 Bottle Caps if your Barter is high enough) Bottle Caps to Ahzrukhal or by killing. This is a ghoul store.

The bar is owned by Ahzrukhal. The bar is rivaling with another store in the underworld over customers. Thus the reason why Ahzrukhal will give you Charons contract for killing Greta in Carol's.