When one of their tightly-knit group mysteriously disappears, four high school girls find their friendship difficult to maintain when they begin receiving taunting messages from someone who seems to know everything about their past and present secrets.

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.

Former best friends Emily, Aria, Hanna, and Spencer continue to live in fear as they struggle to keep hidden even more secrets and someone new begins stalking them via their cell phones.

"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...