The Trimoni Twins can't wait to perform their magic show in the famed Merlin Hotel in Amsterdam. There they meet their tutor Hector's interesting and eccentric uncle Hoogaboom, who is in the business of creating miniature scale models of all kinds of things, including houses and famous buildings. They befriend Uncle Hoogaboom and soon discover that Hoogaboom's special creations are the products of more than skill and craftsmanship; he makes them with the legendary Shrinking Coin, which has been handed down through his family for generations. But the Shrinking Coin isn't his only secret, and the girls are quickly embroiled in an international mystery that can be solved only with their trademarked ingenuity and teamwork. And a little ka-poofing, of course.