Luke Harrison's dad makes horror movies. It is a lot of fun being around a lot of such scary stuff - especially when you have your own monster museum at home. But when two ventriloquist dummies - Slappy and his twin Snappy - join the collection, things get real creepy. Real-Life creepy! Slappy and Snappy can walk and talk on their own. And they can make you scream on their own. They have a plan to make everyone's lives miserable. Will Luke be able to stop this terrible twosome?
Prologue: 1920- Mahar is a puppet maker, and he worked with the magician Kanduu. But Kanduu used magic to bring Mahar's dummy, Mr. Wood, to life. Mahar runs away, and lives a life of his own, creating dummies. A group of townsfolk come in and take his dummy off of his desk and then burns it.
Mahar then goes to his back room, and talks to his "real" dummies, Slappy and Snappy. Then, they all laugh at the townsfolk who thought the doll they burned was really causing all of the trouble on the farm.
Today- Luke Harrison has a science project to build with his sister Kelly, and his friend Jamal. Their dad makes horror movies in the Hollywood Studios, and he keeps many of his movie props in the basement and in the attic. In the garage, Luke and his friends notice two ventriloquist's dummies standing side-by-side and talking and making jokes. Luke asks if it is his dad pulling a prank, but there is no answer.
When his dad shows up in his car, the dummies sprawl lifelessly on the ground. Luke's dad takes the dummies up the attic, and explains that he bought them from an antique store. He plans to sell them to two different buyers after he uses them in his next horror movie. He tells the kids that he will have them in the movie as crowd extras, and that the film will be called "I Married a Dummy".
Later, when Luke's dad leaves, the dummies start to tap on the glass, and the kids unlock the glass case that they were in. They said that they heard Luke's dad say that he was going to separate them, and that they plan on attempting to hurt him for trying to separate them. Slappy is the dummy with the green eyes, and Snappy is the dummy with the black eyes. Slappy is mean, but Snappy is always trying to be nice, and keeps on telling Slappy to be nicer to people when they talk to him.
But, Slappy doesn't like it when Snappy is being nice. The kids try to videotape the dummies being alive, but every attempt fails. Luke's dad never believes that the dummies are alive, and he keeps growing angrier every time they try to get him to see. Later on in the story, Luke notices that the propane tank is missing from the garage, and he suspects that the dummies took it when his dad put them in the car to go the the film's shooting.
It turns out that Luke's dad put the propane tank further away from the house for safety. When the kids come back, they notice that the dummies hid in the trunk of the car that brought the kids home. The dummies start fighting, and Slappy and Snappy go closer to the propane tank. Slappy then lifts up Snappy and hurls him into the propane tank, which created a fiery explosion that takes out most of their garage.
The dummies fly out in different directions, and then Luke's dad shows up. He tells them that he came home shortly after, and that he saw the dummies come to life and started arguing. He apologizes for being so mean to the kids for not believing them. One dummy flew far past the treeline beside the house, and the other one falls in the grass of their backyard. The dad plans to throw the one dummy away, but then the kids tell him that there was a mean dummy and a nice one, and that he should check the dummy's eye color.
They find that it is Snappy, the nice one with the black eyes. Once Luke replaces Snappy to the glass case, he asks him if he will continue to be a good dummy. But then, Snappy tells them that Slappy thought that it would be funny if he acted nice as a joke, and he plans on making their life into a living horror movie. He decides to call it "Snappy Rules!"
Epilogue- Slappy tells the reader not to worry about him, for he will be back in another Goosebumps book, and that this is SlappyWorld, where one only screams in it.
I Am Slappy's Evil Twin received an audiobook adaptation on September 26, 2017.
|Audiobook||Release date||Length||Narrated by|
|September 26, 2017||2 hours 50 minutes||Joe Fria, Aaron Landon and P.J Ochlan|
- The pre-release cover art has several differences from the final version. The main differences being brighter lighting and less-saturated green.
- This book reveals Slappy's and Mr. Wood's origins.
- This book was first announced by R.L. Stine during an interview, and later confirmed by Scholastic's website. 
- Luke's father's name is mentioned in the book, David Harrison.
- The title sounds similar to the Goosebumps Series 2000 book, I Am Your Evil Twin.
- This book, similarly to the Goosebumps Most Wanted: Special Edition books, starts with a prologue.
- The book references Lego, Warner Bros. Studios, and Disney.
- The horror film that Luke's dad is making during the book is called "I married a dummy". This might be a reference to the Goosebumps Series 2000 book Bride of the Living Dummy.
- Slappy interrupts the plot four times in this book.
- ↑ I Am Slappy's Evil Twin (Amazon) (mirror)
- ↑ SlappyWorld Interview: "I Am Slappy's Evil Twin"
- ↑ SlappyWorld Book #3 (Scholastic Website)
|Goosebumps SlappyWorld series|
|#01 Slappy Birthday to You||#05 Escape from Shudder Mansion|
|#02 Attack of the Jack|
|#03 I Am Slappy's Evil Twin|
|#04 Please Do Not Feed the Weirdo|