When thirteen-year-old Cassie Keller (Emily Osment) was going to the library, she caught a glimpse of a Halloween store and the store owner gave her a book entitled The Evil Thing. On its front page was the warning DO NOT READ ALOUD. Cassie ignores the warning, and reads it to her younger brother, Max. The Evil Thing is later brought into reality and kidnaps Max when he started to think about it. It also captured Priscilla and a nameless pizza delivery man. They were to be food for the Creature's offspring when they were born.
Cassie, along with Sean, go to the Halloween shop to find out how to defeat the creature. The man later gave them a riddle; it was: Two heads are better than one. That's the way to get the bloody job done. They later come up with an idea to get a roast that Cassie's mom was cooking and throw it onto the monster. The monster would then have no other choice but to drain itself dry of its own blood. Due to some minor problems, they end up dumping the blood on Max. Max then faces his fear of the Evil Thing and tosses the blood onto the monster. It soon starts to attack its own heads and explodes, talking its offspring with. Cassie and the others freed the pizza delivery man, and Priscilla, and Sean severes his ties with her. However, the Evil Thing is brought back to life when the Cassie's parents find the book in the fireplace. The lights in the house soon went out, and the movie ended with the Halloween shop owner telling the audience to have a Happy Halloween and then proceeding to laugh maniacally.
This was the poem that brought The Evil Thing to Life. It goes as follows:
"The Evil Thing is a gruesome beast. On living flesh it loves to feast.
It's a two-headed thing whom you don't wish to greet.
One head sucks your blood, one head chews your meat.
It carries its babies in slimy eggs on its back.
The babies are hungry when they hatch for a snack, so
the Evil Thing traps some poor victim alive, for the babies to eat when their birthdays arrive.
But don't worry, don't cry, please don't have a fit.
''The Evil Thing is not real... unless you think about it."