Revealed is the tenth and final episode of Season 1.
'C' calls out all The Liars to meet at the masquerade ball.
To all the Liars: Masquerade Ball. Be there when the clock strikes midnight. -C
Meanwhile, Sam and Mona go follow the address, while Jenna, Clara and the other Liars search for 'C' at the ball.
After Sam and Mona arrive, Sam breaks down the door, and they see C's lair. It's full of pictures of CeCe, wigs, and items. After Mona gets some gum and says she'll call Clara, and Sam is nodding and looking around. About 10 minutes later Sam looks at some items, and notices something that he gave to Mona. He then puts the pieces together, and says "You didn't really call Clara did you? Because you're C!" and he turns around abruptly.
Mona is seen wearing the "C" black hoodie.
Mona: Congratulations Sam, you've figured it out. I new a smart guy like you would eventually put the pieces together.
Mona slaps Sam and knocks him unconcious.
Sam wakes up in Mona's car, which is going very fast. Mona threatens Sam, and attempts to blackmail him to join The C-Team, but instead he secretly video calls Clara and points his Camera at Mona. Mona is then exposed, but she doesn't realize it at first. The other Liars see where they are, and get in the car to follow Mona and Sam.
Just as Mona and Sam are about to go over the edge of the cliff, the car of the other Liars show up and stops it. Mona then tries to attack Sam and throw him down, but Clara is crying and at the same time trying to get him free of Mona's grip. Mona then slips and Sam holds out a hand.
She is dangling over the edge holding Sam's hand, and Sam loses the grip. "MONA!!!" he calls and she falls down the cliff.