It's midnight, Yoyo, Gluglu and Bibou are not in bed, they're out playing acrobats! But is it safe to go out at this hour? Do they know that when the moon is round, strange creatures roam in the dark and growl? "Not even scared, not even scared!" scream Les Pyjamasques. But what is this beast? Les Pyjamasques fight the Grogarou that looks like a big nightmare and give small readers the feeling of being able to overcome their nocturnal anxieties.
The book begins with the Original Les Pyjamasques wandering through the night doing their acrobatics as the clock strikes at midnight.
The Original Les Pyjamasques were interrupted by Grogarou who roared at their faces, but the heroes proclaimed that they are not afraid of him and retaliated by screaming at him which caused him to fall backwards with surprise. Then the Original Les Pyjamasques started playing around with him, wondering who Grogarou is.
Angrily, Grogarou threw them off his back and reveals his plan that he is going to eat the heroes raw as stated that during the full moon he becomes a werewolf. With that, the Original Les Pyjamasques try to evade pursuit from Grogarou, Original Bibou tries using his cape to trip Grogarou, but he is unfortunate as his cape was caught by the monster who attempts to eat him while protesting that he has school tomorrow. With bravery, Original Yoyo and Original Gluglu rush to Original Bibou's rescue by lunging at Grogarou, and this caused Original Bibou to break free from Grogarou and used his wings to hide the moon.
Due to the result, this caused Grogarou to shrink into Ptigarou. However, the Original Les Pyjamasques prefers him to be at a "petite" format in which Ptigarou agreed proclaiming that he feels lighter.