Morgan Kole and Harry Styles. Best friends turned enemies. Enemies turned step sibilings. Step siblings turned partners in crime. Who knew that the person you hate could change your life?

Four girls whose clique falls apart after the disappearance of their queen bee, Alison DiLaurentis. One year later, they begin receiving messages from a mysterious figure using the name "A" who threatens to expose their secrets. At first they think it's Alison herself, but after she is found dead, the girls realize that someone else knows their secrets, â€" including long-hidden ones they thought only Alison knew.