<p>Aria, Emily, Spencer, Hanna and Alison have been best friends since the third grade. They go everywhere together, thinking no-one can come between them. If anyone is the ringleader of the group it is Alison, and the other girls cannot help but confide all their secrets to her.<br><br>One night, during a sleepover, Alison goes missing. Her body is never found. The girls mourn her death but move apart after time, assuming their secrets have disappeared with Alison too.<br><br>Three years later and Aria is having an affair with her teacher; Emily is questioning her sexuality; Hanna is a thief; and Spencer is flirting with her sister''s fiance. They all think their secrets are safe, until they starting receiving messages from the mysterious A - who knows exactly what they are all up to, and is threatening to spill the beans . . .</p>