From the publisher's website:
"Several centuries past, a shadowy sect sought to enslave the world in the name of their dark lord, Baalzebul, one of the arch devils of Hell. They carved out a massive subterranean temple. The clerics of Tyr were eventually able to raid the temple before their ambitions could be fully realized. Cut to the present: A company of clerics calling themselves the Order of the Black Lotus have journeyed to the evil fane with the intent of reviving the forgotten cult of Baalzebul. It is up to you to see that they don't fully unite with the undead servants of Baalzebul, unleashing the arch devil's horde upon an unsuspecting world. This product is designed for 4-6 player characters of levels 13-15, and contains a detailed key and maps to the sprawling three level underground Temple of Baalzebul. Also includes a new spell, a new monster, and rules for the worship of the arch devil Baalzebul."