It seems like only yesterday that Hanna Marin, Alison "Ali" DiLaurentis, Spencer Hastings, Aria Montgomery, and Emily Fields were carefree, fun-loving seventh graders at posh private school Rosewood Day. Planning sleepovers, gossiping about boys, braiding each others hair, sharing secrets. But like the flip of a switch, everything changed. Ali mysteriously disappeared, and the four other girls parted ways. That was years ago. Now the mysterious "A" has dredged up the past once more; barraging Hanna, Spencer, Aria, and Emily with painful memories of the past via text messages. It's obvious that "A" is Ali's killer; but if the girls tell, one of them will be the next to die.
Hanna Marin has always been so full of life. Shopping as much as possible, prancing around in sky-high platforms, and perusing fashion and gossip websites to get her daily fix of all things celebrity. Seeing her lying in a hospital bed, unable to speak, bruises dotting her face, in a coma seems completely out of the ordinary. Aria Montgomery, Spencer Hastings, and Emily Fields know Hanna, and this isn't her. But it is a reminder of just how close "A" truly is to them; and how "A's" threats are absolutely true. But Hanna isn't the only one in turmoil at the moment.
Emily Fields has suddenly been shunned by her family. The fact that she has come out of the closet, so to speak, shames her parents, and even her sister, and has landed her on a one way trip to Iowa to live with her strict aunt and uncle, along with their children. Iowa seems like the worst place on earth. But some of the people there are actually pretty cool; and very into Emily.
Spencer Hastings has finally come to the realization that she has black-outs at times, and can't help but wonder if she is the one responsible for Ali's death. With the Golden Orchid competition coming up, however, Spencer has no time to think about the past - only the future. After stealing her older sister's essay, and having it nominated for the Golden Orchid, Spencer can't believe that her family is supporting her in this competition. But it's up to her to do them proud. Too bad she has a strange feeling that somehow, her lying, stealing, cheating ways are going to come back to haunt her.
Aria Montgomery wants nothing more than to be with her older teacher, Ezra. But after "A" spilled the beans about Aria and Ezra's little affair to Aria's boyfriend, that's impossible. Suddenly, Ezra is under scrutiny, and Aria has been cast out of her temporary living space. The only thing left for her to do is to turn to her cheating father, Byron, and his artsy girlfriend, Meredith. But turning to the two of them is right up there with selling your soul to the devil, and Aria doesn't know if she's ready to do something so drastic. The four girls now realize that Mona Vanderwaal is A. Mona tries to kill Spencer while Hanna,Emily and Aria contact Darren Wilden. After an intense fight about Ali, Mona is killed.