Young Brian is struggling to adjust to his new life after moving to a new town with his family. His frustrations peak when he begins to encounter strange occurrences in his bedroom at night. Determined to uncover the cause, Brian sets up an elaborate trap and discovers Maurice, an impish monster living under his bed. Maurice introduces Brian to a fantastical world where monsters roam freely and play mischievous pranks on unsuspecting children. Maurice and Brian quickly form an unlikely friendship, bonding over their shared love of fun and mischief.

However, as Brian delves deeper into the monster realm, he begins to realize that the playful antics come with darker consequences. The seemingly innocent pranks start to have negative impacts on his real-life relationships and responsibilities. Haunted by the chaos caused by the monster world, Brian finds it increasingly challenging to balance his dual lives. Suspicion grows as Brian's behavior becomes erratic, making it difficult for him to convince others of the hidden dangers lurking just beneath the surface of their everyday world. The line between reality and fantasy blurs, leading Brian to confront the crucial decision of which world he truly belongs in.