Can anyone please help me out. When i was twelve or so i read

File: question-mark-on-a-circular-black-background_318-41916.jpg (24KB, 626x626px) Image search: [Google]

24KB, 626x626px

Can anyone please help me out. When i was twelve or so i read this book that i really liked. the book had really heavy sexual and criminal themes which blew my cringey faggot tier mind at the time. Problem is i dont remember the title so i was hoping one of you might know it.

>book centers around woman who randomly finds a letter in a library.
>letter contains 50 dollars and says that every letter after this one will contain double the reward of the last.
>50 to 100 to 200 to 400 you get the idea.
>basically the premise is that as the reward gets larger the letters become harder and more dangerous to acquire.
>at one point she has to fight off vicious dogs in a graveyard.
>she breaks into a mansion at one point and finds a bunch of missing teenagers who are now sex slaves for the owners of the mansion.
>I'm pretty sure she gets a boyfriend at one point and he gets his finger chopped of but I'm not sure.

Was just hoping one of you might know the title to this book cause i want to re-read it for nostalgia value. Thanks heaps