Here's a summary of the ending:
* The girls are finally starting to feel like they are getting close to figuring out who "A" is. They think they have narrowed it down to two suspects.
* Spencer is caught in a compromising position with Melissa, her sister's boyfriend, and feels betrayed.
* Aria discovers a secret about her father that rocks her world.
* Emily starts to develop feelings for Maya, but their budding relationship is complicated by Maya's past.
* Hanna is dealing with the fallout from her mother's addiction and trying to find her place in the world.
* The girls find a secret lair that they believe belongs to "A" and find clues that connect to their past.
* Suddenly, "A" appears before the girls in the lair and reveals that they are closer to discovering their identity than they think.
* The book ends with "A" warning the girls, "You're playing with fire. And fire burns."
This ending leaves readers with many questions. Who is "A"? What do they want? And what will happen to the girls now that they have been found?
The cliffhanger sets up the third book, "Perfect," which continues to explore the mystery of "A" and the girls' search for the truth.