怪物先生远离城镇孤独地生活，陪伴他的只有一个神秘的家伙。两人自幼在一起，无忧无虑，倒也相安无事。直到一天，神秘伙伴给他惹了麻烦，让他在众人面前丢尽脸面。可怕的梦魇吞没了怪物先生，让他无法逃脱。从梦中惊醒的怪物先生将自己和神秘伙伴禁锢在房子里，试图封闭与外界的一切联系。一场意外大火降临，怪物先生进退两难。

Mr. Monster lives a lonely life away from the town with his only friend, the Mysterious, who grew up with him happily and peacefully. Until one day the Mysterious causes some trouble and makes Mr. Monster embarrassed in front of everyone, and trapped in horrible nightmare. Mr. Monster tries to cut off all contact with the world by locking themselves in the house. Unfortunately, an unexpected fire comes, and Mr. Monster is in a dilemma.