ABC Family's Pretty Little Lairs
is a big hit but before it was on television it was a successful YA book series 
by Sara Shepard
However being that tv shows do take a different paths than book (its reviled who is A in the book) it doesn't mean the show going to be the exact. So you may have to continue watching it and see what the producers have in mind.
But for those of you have read the books would be happened to know there is a Pretty Little Lairs Tv tie-in novel
so who knows there's another set of novels to the series.