SOLVED. Novel's title is something about a handbook for young ladies [s]

[Y]

Don't remember what exactly it was about but it was pretty dark; the heroine finds out in the end that her father was trapped for 20 years in some cult that has orgies, but by doing so they share the consciousness and become some super-powerful stream of knowledge that he wanted to tap into.

[Amy (Other Amy)]

Possibly The Diamond Age: or, A Young Lady's Illustrated Primer. (I haven't read it yet, but it sounds like it could fit.)

[Lobstergirl, au gratin]

When did you read it? A range of years is fine. Standalone or part of a series? Remember the cover? Author male or female? YA, adult?

Paper book, ebook, other format?

[Y]

Yes yes yes Amy it is! And thanks Lobstergirl too :)

[Amy (Other Amy)]

Yay!