- Deborah Scorsone as Lucy Dark
- Eugene Lipinski as Mr. Mortman
- Christopher Tuah as Aaron
- Lynne Cormack as Mrs. Dark
- Dan Lett as Mr. Dark
- Brandon Bone as Randy Dark
Lucy loves telling monster stories, but her family and friends are tired of her wild tales. So when Lucy sees a real monster—Mr. Mortman, the local librarian—no one will believe her. If she can just get proof that he is a monster maybe then they'll listen. But is it too late? Mom and dad have invited Mr. Mortman to dinner! This is sure to be one meal that'll be hard to swallow.
Differences from the book
- In the book, Mr. Mortman keeps pet turtles, but in the episode, he keeps pet spiders.
- The scene where Lucy goes to Aaron's house and meets his brother is not depicted in the episode.
- The scene where Lucy and Aaron follow Mr. Mortman home is not depicted in the episode.
- There is an extra scene after Mortman is eaten, where Aaron appears with a monster mask and later takes it off when Mr. and Mrs. Dark had brought out their fangs, he asks what is for dessert. Mr. Dark then answers with, "You....like Cherry Pie?" and the family laughs.
- In the book, Mr. Mortman mainly eats flies. However, in the episode, he eats crickets instead.
- In the book, Aaron sees Mr. Mortman turn into a monster and him telling Lucy's parents is what convinces them that Lucy is telling the truth. In the episode, this does not happen and instead Lucy's parents invite him to dinner after bumping into him at the photo place.
|Title||Release date||Media type|
|September 16, 2008||DVD|
|August 26, 2014||DVD|
- This episode, along with "The Cuckoo Clock of Doom", on their original premieres, had a special opening theme in which there was a ten-second remix when R.L. Stine is walking through the grass with the briefcase. When the G passes the dog, that part of the music is played with a different instrument. There were also different scenes from the television show, when the door opened.
- Mr. Mortman's actor, Eugene Lipinski, later voiced Rocky in "Night of the Living Dummy III".
- The music Mr. Mortman hums is none other than the famous song A Little Night Music.
- While "The Cuckoo Clock of Doom" was the first proper episode to be aired, this was the first one produced. 
- The Goosebumps Presents books adds an addtional moment to the ending, where Aaron asks to see Lucy's monster picture and they joke that the reason why she doesn't have it is hard to swallow.