What happened when Alison from Pretty Little Liars left the barn?

Answer 1

First off, you find out in the last book that the girl that the Pretty Little Liars were friends with wasn't really Alison. It was her twin sister Courtney who was certifiably insane. When the girls showed up in Ali's backyard for the Time Capsule piece, Courtney came out pretending to be Alison and when her mother came out to say they were leaving, they were taking Alison to a mental hospital. In short, they SWITCHED places. Alison being mistakenly taken to a mantal hospital; Courtney taking on Alison's identity.

NOW. At the sleepover, Spencer and Courtney argue and then Courtney runs out to meet Ian. But on the way, Alison pops out and kills her sister(for ruining her life), shoving her into the hole and then runs away.

Hope this is clear, if not, read the books. They are AMAZING! Better than the TV show.