Alison, Aria, Emily, Hanna and Spencer were best friends, until Alison disappeared. Three years later, the remaining girls, now juniors at Rosewood Day, are leading separate, but charmed lives.
After living in Iceland, Aria returns home sophisticated and worldly. Emily is a champion swimmer, Hanna is the most popular girl in school, and Spencer's accomplishments make the average type-A valedictorian look like a slacker. But in Rosewood, appearances are deceiving, and when the girls start receiving mysterious texts signed by someone named A, the past threatens to ruin their perfect present. A claims to know all of their secrets—but who is A? How much does A really know? And what can four pretty little liars do to protect themselves from the truth?