"The Evil Spirit of Mr. Descartes" is a captivating children's book that takes young readers on a philosophical journey. On a cold winter night, the famous thinker René Descartes is plagued by doubts. He wonders whether fundamental mathematical truths, such as the sum of two and three, are actually correct. This story not only stimulates the imagination but also encourages critical thinking and curiosity in children. The author, Jean Paul Mongin, who has a passion for philosophy, tells the story with a touch of humor and a hint of seriousness. The illustrations by François Schwoebel complement the text and make the book a visual experience. Ideal for children aged 10 and up, this book offers an entertaining way to engage with fundamental philosophical questions and unleash one's imagination.