"Unbelievable" Summary

The book that I'm currently reading is "Unbelievable" by Sara Shepard. The book is about a group of four girls, Aria, Emily, Hanna, and Spencer, who's best friend Ali mysteriously disappeared 3 years ago. Now 3 years later cops find Ali's body dug up in her backyard. After finding Ali's body, the four girls start getting mysterious texts from someone named "A" that, somehow, nows each and every little thing about the girls. The texts start getting worse and worse, leaving one of the girls in the hospital. Follow the girls in the fourth book in the "Pretty Little Lairs" series.