In Rosewood, Pennsylvania, four stunningly beautiful girls are haunted by a very ugly past. Spencer, Aria, Hanna, and Emily want nothing more than to forget Alison DiLaurentis, their former best friend who tried to ruin their lives. But someone refuses to let her memory die. A is still out there, lurking in the shadows and digging up the pretty little liars' newest secrets.

Emily's reconnecting with an old flame, one baby step at a time. But is she headed toward true love or another bundle of heartache? Spencer's learning about the highs and lows of campus life on a trip to Princeton. Aria's seeing a whole new side to Noel's dad—and it could drive a wedge between her and Noel. And, for better or worse, Hanna's getting in touch with her inner A.

Secret by secret, lie by lie, the girls get tangled in A's dangerous web. A knows about everything, from their tiniest transgressions to the awful incident in Jamaica. Soon A will have enough ammunition to pull the trigger and end the pretty little liars, once and for all. . . .