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.

"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...

Struggling to return to normalcy after surviving Alison's attempt to kill them, Spencer, Aria, Emily and Hanna endure a series of disasters before realizing that they are being stalked by a new "A" who knows all of their secrets.

In the weeks leading up to Ali's murder, Ali reveals her plots against Emily, Hanna, Aria, and Spencer, as well as a dark secret that has the potential to destroy everything.

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.

"Deadly, the fourteenth volume in Sara Shepard's YA Pretty Little Liars series, delivers more juicy scandals, dark secrets, and shocking plot twists. This #1 New York Times bestselling series is also a hit ABC Family original TV show. High school seniors Aria, Emily, Hanna, and Spencer have all done horrible things--things that would put them behind bars if anyone ever found out. And their stalker 'A' knows everything. So far A has kept their 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.