ABC Family is making it as clear as possible in its Pretty Little Liars promos for this Tuesday's summer finale: someone is about to commit the greatest betrayal in show history.

Or the greatest betrAyal, we should say.

Who will it be? Let the guessing games begin. In the meantime, check out three clips from "The Lady Killer," starting with a crime scene that leave Hanna in uncontrollable tears:

Elsewhere, Spencer will confront Paige in the school hallway. And the combating sparks will fly:

Finally, Mona only utters four words in this sneak peek. But they're a frightening four words:

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.