'When the Eternal Key hauls Charlie out of his exam room, he knows he's in trouble. Big Trouble. Before Charlie knows it, he is zipped through time to a renaissance castle in Sweden. On a quest to find the truth, he searches for a stolen manuscript, but a demon lurks in the shadows ─ ready to stop Charlie at every turn. Descartes' ideas are Charlie's only chance to triumph, but does he have the mind to survive? Descartes' Demon and the Eternal Key is the second novel in the Eternal Key Series that introduces famous philosophers to children aged 9-12. The time travel adventure story presents Descartes' most famous ideas in an exciting way for children. Ideas covered include: Mind-Body Dualism, the Evil Demon, the Existence of God, the Wax Argument and Cartesian Geometry. The story carries Descartes' overarching idea of the pursuit of certainty ─ "What can we know?" An action-packed book for middle grade readers looking for an exciting introduction to Descartes and his ideas!' (Publication summary)