Spencer pushes Mona off the cliff during their fight.
Authorities arrive, and it is discovered that Mona survived the fall. Dr. Sullivan diagnoses Mona with a personality disorder, and she is sent to a mental institution, Radley Sanitarium.
The episode centers on the Liars (Aria, Emily, Hanna, and Spencer) learning the true identity of the main tormentor, "A." It is revealed that Mona Vanderwaal is A.
Mona tricks Spencer into going to a cliff-side "A's" lair (near a hotel area). Mona tries to force Spencer to join her "A Team," and when Spencer refuses, a struggle ensues.