Season 1
The first season of Pretty Little Liars, based on the books of the same name by Sara Shepard, premiered on June 8, 2010 and concluded on March 21, 2011 on ABC Family. It tells the story of a clique of five girls - Spencer, Aria, Hanna, Emily, and Alison - until one of them goes missing, Alison. One year later, the girls have grown apart and start getting messages from a mysterious 'A', and thinking it's Alison, they soon find out that Alison is dead, and someone else is taking her persona. The show will follow the basic premise of the novels.
Season 2
The second season of Pretty Little Liars, based on the books of the same name by Sara Shepard, premiered on June 14, 2011 and concluded on March 19, 2012 on ABC Family.[3] It follows the lives of four teenage girls, Aria Montgomery (Lucy Hale), Spencer Hastings (Troian Bellisario), Hanna Marin (Ashley Benson), and Emily Fields (Shay Mitchell), who are dealing with the mysterious disappearance and death of their former best friend and queen bee, Alison DiLaurentis (Sasha Pieterse), along with other problems in their personal & social lives. Outcomes of Alison's death include messages from an anonymous source that we know as "A". This person knows everything about the girls, including some terrible things that they did in their past with Alison. The second season continues from the season finale of the previous season, in which Ian Thomas (Ryan Merriman), Spencer's brother-in-law, is presumed to have been killed in an incident at the top of a bell tower but is also accused of murdering Alison.