The elderly Italian craftsman Guido and his granddaughter Mona run a plaster cast shop in a nordic city. Pat and Patachon serve as eager helpers, wholeheartedly dedicating themselves to the work. Among the shop’s customers is a young actor, Kaj Lynge, who spends all his money on plaster figurines just to visit Mona. Another frequent visitor to the shop is the upstairs neighbour’s son, Theobald, who is a bit of a charlatan. One day, during a scuffle in the workshop, Guido’s ‘lucky mug’ is broken. Inside, they find a rolled-up note pointing to a hidden treasure secreted away by one of Guido’s ancestors. However, the most crucial part of the treasure map is in another mug, which Guido once sold to a fellow Italian in Amsterdam. Propelled by gold fever and a thirst for adventure, Pat, Patachon and Mona set out to find the other mug and thus the treasure.