Pretty Little Liars is an American mystery teen drama television series created by Marlene King. Based on the popular series of novels written by Sara Shepard, the show premiered on June 8, 2010 on ABC Family. The series follows the lives of Aria Montgomery (Lucy Hale), Spencer Hastings (Troian Bellisario), Hanna Marin (Ashley Benson) and Emily Fields (Shay Mitchell), four girls whose clique falls apart after the disappearance of their queen bee, Alison DiLaurentis (Sasha Pieterse). One year later, they begin receiving messages from a mysterious figure using the name "A" who threatens to expose their secrets. At first they think it's Alison herself, but after she is found dead, the girls realize that someone else knows their secrets, & including long-hidden ones they thought only Alison knew.
After an initial order of 10 episodes, on June 28, 2010, ABC Family ordered an additional 12 episodes for season one. These episodes began airing on January 3 and ended on March 21, 2011. The ratings success of the first 10 episodes prompted the book series to be extended beyond the initial eight novels. On January 10, 2011 ABC Family renewed the series for a second season. The second season premiered on June 14, 2011, and after an initial order of 24 episodes, an additional Halloween episode was added as a part of the network's 13 Nights of Halloween lineup bringing the season 2 episode order to 25 episodes.