Middletown resident Sammy Jacobs has always loved science fiction books and films, which causes his parents, who are both scientists, to be always trying to make him like real science. Aside from Sammy, Simon is a kid with a small imagination who, like his parents, love science.
When Sammy meets Brent Green, Sammy keeps trying to convince his parents that Brent is real, but they don't believe him, and this leads them to eventually think he needs a psychologist. Even Roxanne Johnson, his best friend, doesn't believe him.
However, Sammy has an idea to show Brent to his parents. He grabs a Molecule Detector Light, which is a special flashlight their parents developed, and it allows people to see things that you normally can't see. Sammy points the light to Brent, finally revealing his real body. Shocked, Sammy screams that Brent is a monster. It is then revealed that Brent is a normal human who was turned invisible by his mother, and Sammy and all the other characters are actually monsters.
Sammy has a great imagination, and he often daydreams about ghosts, monsters and other supernatural creatures.
As described in the book, Sammy has five eyes, more than one head and several long arms. Instead of hair, he has antennae, tendrils and suction pods in the top of his heads. In the episode, Sammy, like everyone else (besides Brent) look like normal human beings, but can project their faces into the back of their heads.
- Unlike most Goosebumps books, the reader only gets a physical description of the protagonist in the last chapter.