Killer

Killer is the sixth book in the Pretty Little Liars series by Sara Shepard, which was published on June 30th, 2009 by HarperTeen.

Book Summary
The girls discover that the person they think is Ali's murderer — Ian Thomas — has actually been framed, and they start to wonder if the new "A" really wants to threaten them or just to solve the mystery. Emily has sex with her new boyfriend Isaac, whose mother finds out and banishes Emily from their house without Isaac knowing. Hanna and Kate compete for the affections of Aria's brother Mike Montgomery, while Aria falls in love with Jason DiLaurentis again.

Spencer meets a woman named Olivia Caldwell who she thinks is her real mother, and attempts to move to New York, but it turns out to be a scam and she loses her college money. At the opening party for Radley, a former so-called "haven for troubled youth", Emily finds proof that Jason DiLaurentis had been a patient there, and soon Hanna, Aria, and Emily all come to believe that Jason and Darren Wilden had something to do with Ali's murder.

an Thomas confirms their suspicions about Darren and Jason right before someone sets the woods behind Spencer's house to fire. While Aria is trying to get to Spencer's barn to show them Ali's flag from 6th grade, she finds someone caught in the woods because of the fire, saves this person, and then they all recognize her as Ali.

Messages from "A"
Dear Spence, When I told you that he had to go, I didn't mean he had to die. Still, there's something really sketchy in this case...and it's up to you to figure out what it is. So better get searching, or the next one "gone" is you. Au revoir! --A

One of these things doesn't belong. Figure it out quickly...or else. --A

Enjoy your gimlets? Well, sorry, darling, but the fantasy's over. Big Brother is hiding something from you. And trust me...you don't want to know what it is. --A

Dear Little Miss Spencer-Whatever-Your-Name-Is, Shouldn't you know by now what happens if you don't listen to me? I'll use small words this time, so even you'll understand. Either give Long-Lost Mommy a rest and keep searching for what really happened...or pay my price. How does disappearing forever sound? --A

I guess we all have stuff to feel guilty about, huh? --A

Too distracted to decipher my clues? Go to your first love's old house and maybe it'll all make sense. --A

What do you think HE'S so angry about? --A

Break-ups
In this book Emily and her boyfriend's mom metaphorically break up.

Emily and Isaac break up because when Emily told Isaac his mom was trying to get rid of her, he doesn't believe her. Later, Isaac realizes Emily was telling the truth, he tried to get back together with her but Emily said that she didn't want to forgive him because he didn't believe her at first.

Hook-ups
Hanna and Mike (Aria's little brother) hook up.