"The Uninvited" - Anna Rydell returns home to her sister (and best friend) Alex after a stint in a mental hospital, though her recovery is jeopardized thanks to her cruel stepmother, aloof father, and the presence of a ghost in their home. Image and info credit: IMDb.
I generally don't care for books with an agenda but Liz Jensen's agenda is revealed with such creepiness that I was hooked. The genius is that her main character whose life is ruled by facts and truth (he has Asperger's Syndrome) now lives in a world that is no longer logical. I won't give away the agenda but I think it is two-fold. You should judge for yourself. Enjoy!