Partial spoiler alert!!!!
Lured by sex, the protaganist finds he cannot escape the coven. He's been chosen to fulfil a specific role and if he cannot complete the task given to him, he will be replaced. Within this context the protaganist works at freeing himself from the group and leader that have bound him to their purpose.
Plenty of occult rituals with a Satanic philosophy underpinning the workings of the coven; might is right. There are however aspects that modern Satanic groups would find contentious.
With that said, the book is well worth a read to anyone interested in the occult.
As with his other two books, I have read this a few times over the years.