"Based on Sara Shepard's popular novels, this ABC Family series follows four high school girls -- Emily, Aria, Hanna and Spencer -- whose longtime friendship has been strained since the disappearance a year earlier of their clique's leader, Alison. A stranger, known simply as "A," has been texting the girls and threatening to reveal their darkest secrets, which they thought only Alison knew. Lucy Hale, Troian Avery Bellisario and Ashley Benson co-star."