This book is the novelization of the Hammer Studios film of the same name. While most novels take the opportunity to flesh out aspects of the story the movie doesn't cover, this only fleshes out one aspect. And flesh is the key word here because the only real difference is explicit sex. This book is flat out smutty. Actually quite annoyingly smutty. Near as I can tell, the only purpose of this book is to remind us that Ingrid Pitt is hot.
For Hammer complete-ists or people who like to fantasize about Ingrid Pitt. Otherwise, don't bother.