Alison DiLaurentis, Aria Montgomery, Emily Fields, and Spencer Hastings all had a sleepover one night the summer before eighth grade.
Toby, the next door neighbor has always been a creep. So one day Alison was over it. She decided it was time to get back at him. She got fireworks and went over to toby's tree house and lit the fireworks off through the window.
Ali! Where did you go? This isnt funny!
The fireworks went off when Jenna, Toby's sister was in the tree house and it caused her to go blind. Toby and his mom talked to the police about what could've caused the tragedy. They had no idea it was Ali.
Hanna, Even Daddy doesn't love you best! -A
The girls soon realized what happened when they seen Jenna being taken in an ambulance. They all promised never to tell anyone and decided to go to sleep for the rest of the night.
In the middle of the night a storm comes and wakes Spencer, just to find out that Ali is missing. Alarmed Spencer tells the rest of the girls, and they all go looking for Ali but have no luck.
Throughout the rest of the story all four girls get messages about what they call "the Jenna thing". This mysterious person by the name of "A" is the sender . Of course all the girls assume it is their missing friend Ali but never find out who it is.