After their recent encounter with "A," Aria, Emily, Hanna and Spencer think they may be closer than ever to figuring out whom "A" really is. But when the girls decide to enlist Caleb's hacking skills to help with their quest, Hanna no longer wants a part of the plan. The last thing Hanna wants is to get Caleb involved in something else shady and also to open the door to questions that Hanna can't answer. Once the girls realize that "A" has a helper, Hanna has no other choice. Instead of focusing on figuring out who the "helper" is, Hanna decides to put all of her efforts into throwing a surprise party for Caleb. But will a surprise party at Spencer's lake house be the diversion Hanna is looking for, or just a recipe for disaster? Meanwhile, Aria and Ezra must deal with the aftermath of coming clean.