After Timmy tells Poof a scary story, the baby's' crying keeps him up all night, so Timmy wishes for no light for twelve hours of day. Little does Timmy know, that when his godparents are kept in the dark for longer than eight hours, they become "Scary Fairies" and turn on their godchild.
After Timmy finished reading to Poof "The Super Scary Boogie Monster Who Lives Under Your Bed and Will Totally Eat You When It Gets Dark", Poof starts crying, and a storm starts in Timmy's room, flooding it. Wanda scolds Timmy and Poof asks for the night light, which is so hot that it could burn through metal. Timmy wishes to turn it off so Poof goes scared to the fishbowl and locks it up. But he didn't let Timmy sleep and he only slept 12 seconds. So a very sleepy Timmy wishes for 12 hours with no light.
After the wish, Wanda tells him that after 8 hours with no light, fairies turn into scary fairies and eat their godchildren, but Timmy thinks she just said that for revenge. After 10 hours he wakes up, in a cauldron and sees that Cosmo and Wanda are trying to eat him, so he escapes downstairs where he bumps into his parents. There, a lost Chet Ubetcha tells them that 3 Saber-Toothed Tigers With Night Vision escaped from the zoo. The tigers appear and attack Mom and Dad. Timmy runs away back to his room, where Wanda tells him they are back to normal, but Timmy turns on his torch and sees they're still scary, and runs out of his house and falls, and at the bottom Dad tells him he moved his house up to a hill for the view.
Suddenly, a bus drove by Cosmo and Wanda attempts to crash into Timmy, and they do the same with a train and when they fly a plane, his pajamas get stuck on the wheel and in mid-air he falls and lands on a trampoline, where he finds Crocker hanging from a rope from a helicopter piloted by Mrs. Crocker giving him a flourescent F, which attracts the tigers and he gets mauled. Tootie phones Timmy and tells him she is near, when she appears, Timmy tries to run but hits a wall and faints.
At the hospital he learns he was unconsious an hour so he is half-hour left until light comes back and that Tootie saved him by giving him CPR. He escapes but keeps running into Crocker, Tootie, the tigers, his parents who are still recovering from the tiger attacks (and looking like mummies), and Cosmo and Wanda, who at this point are hideous monsters. But when he is rounded by Tootie, scary Cosmo and Wanda, Crocker, his parents and the tigers at the edge of the hospital's roof, with 10 seconds left, he shouts and manages to get in time. Before Mom and Dad,Tootie,Cosmo and Wanda and the 3 saber-toothed tigers get to Timmy,he screamed and everything was back to normal.
He is suddenly in the front of his house, still scared, where Wanda,Poof and Cosmo were there and Wanda tells him she made up the scary-fairies to make him learn he shouldn't scare Poof. Timmy apologizes to Poof and is about to go enjoy the fresh air, but falls from the hill and faints, and Tootie goes to give him CPR.