The main character, the monster Dennis, believes that human children are under his bed and will get him as he falls asleep.

Some of the books came with an extra plush toy of Dennis with his pillow and teddy bear in each arm.

The introduction starts the book in the setting of a small picnic of a human and his dog.

The human is apparently telling the reader to not venture into the Withering Wood, a forest of trees rumored to have legendary creatures such as hairy trolls, nasty gnomes, and scary pixies and fairies.

[5] As Dennis falls asleep, a young boy skips school and ventures into the Withering Wood to hide (presumably from his parents).

He changes into his night clothes and begins to fall asleep,[7] but the boy was afraid of monsters.

[8] The book then explains not to misbehave and how it would feel if Dennis's mother would tell the reader if humans were not real.

[9] Dennis is a polite,[3] green, cave-dwelling reptilian monster that resembles a Velociraptor.

As the main character of the story, he has many human-like features, such as smiling,[10] walking,[10] and emotion.

[3] A caring mother, she tries to get her son, Dennis, to sleep on top of his bed and to discontinue his fear of humans.

[3] The mother has many human mother-like qualities, such as her purse that she is seen carrying in the beginning of the book.

On the day of Dennis's refusal to sleep, the boy had skipped school, described in the book as hooky, and had hid in the forest.

These include: There are two major morals in The Monster Bed that can both give children two lessons.

[8] Another possible moral is to teach kids not to skip school, as the small child did,[6] and to not try to hide from your parents in areas you do not know.

Some were excited their child had begun reading,[19] and some loved the illustrations, plot, and characters.

Susan Varley even added a small easter egg to her illustrations—a closer look at Dennis's many toys everywhere in the house reveals that they are the same creatures as seen in Where the Wild Things Are.

[13] Some editions of the book come with a plush toy of Dennis, the main character, with a teddy bear in one hand and his pillow in the other.