After their friend who has been missing for more than three years turns up dead, four former best friends continue to receive frightening messages from someone who knows damaging secrets about them.

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 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.

Aria's love life is on the Fitz--ahem, fritz. Emily's exploring her wild side. Hanna's kissing the enemy. And someone from Spencer's past--someone she never thought she'd see again--is back to haunt her. But none of that compares to what these pretty little liars did on their last spring break. It's their darkest secret yet. And guess who else knows?

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...