what book I am searching based on my few memories?- an investigator tries to infiltrate a cult to rescue a young person. (not original I know) However, the interesting bit is that the cult is some sort of weird cannibal affair. They sacrifice parts of themselves and they eat in feasts. I remember the investigator (or friend of) had to have a finger chopped off and it was then cooked and eaten. I also remember a grotesque image of a person who was little more than a head and few basic organs and they were to make a final sacrifice and be eaten. Ideas? it's really bugging me that I can't remember.