There were five friends. One of them, Alison DiLaurentis, was a real jerk, but the other four worshipped her anyway. One night, Alison disappeared. The rest of the girls lost touch, but one year later, the four remaining friends came together on the day Alison’s dead body was found. That was also the day the mysterious “A” started sending them text messages, taunting them. The text messages included secrets about the girls that each girl had only revealed to Alison. So the show has two mysteries: Who killed Alison and who is A?
​

to read more go to:

http://becausewewatchtoomuchtv.blogspot.com/2011/06/summary-of-pretty-little-liars-season.html