Jack (Roddy Piper) is a building superintendent, Jack is a simple man with simple needs. He just wants to be left in peace so that he can get on with reading his book. But the tenants living in his building are always in need of him for something. Fix this, replace that, unblock this toilet.
However, when the power goes out in the building the culprit is not a blown fuse or faulty wiring it is two of the tenants who have opened a portal to hell in the basement of the building. If Jack doesn't close the portal and stop Great Cthulhu rising from his watery tomb city then the entire building, no, the entire world will go down the pan.