"Emily's been shipped off to Iowa to live with her überconservative cousins. Aria's boyfriend is behind bars--because of her. Spencer's afraid she was involved in Ali's murder. But Hanna's fate is far worse: she's clinging to life in the hospital because she knew too much. If these girls don't start listening to me, Hanna's going to look like the lucky one"--P. [4] of cover.

The four former best friends, Spencer, Emily, Hanna, and Aria, try to overcome their friend Ali's murder, but become alarmed when they receive text messages from the mysterious "A" and learn that their friend's accused killer has been released from jail on bail.

After high school juniors Spencer, Emily, Hanna, and Aria think they have seen Ali, their missing and presumed dead friend, they pursue clues from a mysterious stalker, trying to find out if she is still alive.

After their missing friend's body is found and another of their friends commits suicide, four former best friends live in fear of their secrets being exposed by someone who is stalking them via their cell phones.