People think the "Jenna thing" is a pretty cut and dry story, but there is more to the story. Alison had to find an "accidental" way to kill Jenna, but could only do it with a little fib, a tall tale to wet the girls' appetite for revenge. At a sleepover, the girls were trying on each other's clothes. She told them that Toby was spying on them changing and they had to get revenge on him. Alison thought the best way to deal with him was fireworks. She knew Jenna was in the garage getting her Halloween costume ready. She hoped that fireworks would take care of her.
Alison carried an M80 type of firework in her back pocket. She felt it had to have something powerful enough to kill Jenna once and for all. But little did Alison know that Jenna kept a store of fireworks in her garage.
As they entered the outside the garage, Emily and Spencer both had doubts on what she was doing. They relented knowing if they didn't Alison could bring out all their dirty, little secrets in school. There's more that meets the eye when it comes to Alison.
They sneak up to the house. Step by step they take to the garage. Alison seems to have forgotten a lighter.
"Give me a lighter." Alison said insistently
The girls pause shocked at her attitude toward the girls.
"We don't have any." Some of the girls said.
"Spencer. I know you have one." Alison said going up to Spencer's ear, "Remember our promise."
"Here you go Allie." Spencer said scared of Alison.
Alison lights the firework up and tosses it into the garage.
"It was only a stink bomb." Alison said insistently.
They run away from the building and a large, loud explosion comes from the garage. That was definitely not a stink bomb, she threw in the garage. The flames engulfed the garage, the explosion ended up hurting Jenna's vision.