Former best friends Hanna, Aria, Spencer, and Emily, who lost their best friend and leader, Alison, years ago when she disappeared, find themselves in grave danger when they pursue the truth about Alison.

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.

After high school juniors Spencer, Emily, Hanna, and Aria think they've 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 surviving their latest encounter with A, high school seniors Aria, Emily, Spencer, and Hanna must try to convince the police that the real A is still on the loose, all while trying to stay alive.

Even though the disappearance of Alison DiLaurentis has been solved, Spencer, Emily, Hanna, and Aria harbor other secrets which could interfere with their perfect lives, as they try to forget what happened to them in Jamaica last spring.

"It's spring break, and the pretty little liars are trading in Rosewood for a cruise vacation. They want nothing more than to sail into the tropical sunset and leave their troubles behind for one blissful week. But where Emily, Aria, Spencer, and Hanna go, A goes, too. From scuba diving to tanning on the upper deck, A is there, soaking up all their new secrets. Emily is smooching a stowaway. Aria's treasure-hunting partner is a little too interested...