At the end of every schoolday, new teacher Mr Van der Steg entertains his pupils with tall tales of incredible events, which he claims really happened to him - involving hungry lions and haunted castles, shipwrecks and desert islands. One day, when he can't think of anything suitably exciting to tell them, he invents a story about a very important letter which he's expecting that evening, with news of a perilous mission. Evening arrives and so, to his surprise, does an enigmatic letter...And so Mr Van der Steg is drawn into a real-life adventure, featuring a grumpy coachman, a sinister uncle, eccentric ancestors, a hidden treasure, an ancient prophecy and Geert-Jan, a young boy who is being kept prisoner in the mysterious House of Stairs. Although the treasure rightfully belongs to Geert-Jan, his uncle is determined to seize it for himself. As Mr Van der Steg, with the help of his pupils, sets out to rescue the boy, he becomes more and more entangled with the strange history of the Seven Ways, the House of Stairs and the powerful Conspiracy of Seven.