Pretty Little Liars is a series of young-adult novels by author Sara Shepard, beginning with 2006's initial novel of the same name. The series follows the lives of four girls – Spencer Hastings, Hanna Marin, Aria Montgomery, and Emily Fields – whose clique falls apart after the disappearance of their leader, Alison DiLaurentis, in the summer after 7th grade. Later, when the girls are juniors in high school, they begin receiving various messages from someone using the alias "A" who threatens to expose their secrets.
The novels explore several different topics and themes such as bullying, murder, drug addiction, underage drinking, eating disorders, homosexuality, peer-pressure, infidelity, and mental illness. Moral ambiguity and the consequences of lying (suggested by the title) are featured prominently in the series; the girls constantly create their own problems through their unwillingness or inability to tell the truth about certain events and misdeeds they have done.
The novels have appeared on the The New York Times Best Seller list. A television series adaptation loosely based on the novels debuted on June 8, 2010 on ABC Family. The twelfth book in the series, Burned, was released on December 4, 2012. A prequel, Ali's Pretty Little Lies, was released on January 2, 2013. Additionally, a thirteenth book, Crushed,] was released June 4, 2013. Shepard revealed that she is planning on writing three more novels for the series. The fourteenth book, Deadly, was released on December 3, 2013. The fifteenth book, Toxic, was released on June 3, 2014.
The series is loosely divided into four arcs of four to five books each, chronicling the introduction and reveal of each "A". The series follows the lives of four teenage girls — whose names are mentioned above (nicknamed the Pretty Little Liars or simply the Liars) — whose clique falls apart after the disappearance of their best friend, Alison DiLaurentis. Three years after her disappearance, they begin receiving text messages from an anonymous source, "A," who threatens to expose their secrets; including long-hidden ones they thought only their close friend Alison knew. But shortly after the messages begin, Alison's body is discovered. The books progress with the four girls trying to figure out the identity of "A".