Flooded out of their old home, the resourceful Moomin family readily take to life in a floating theatre where many strange things happen, odd even by Moomin standards.
When a flood sweeps through the valley, the Moomins must find a new house. And with typical Moomin good luck, one just happens to be floating by. It looks normal enough, but there are curtains where one wall should be, strange rows of lights, and other odd amenities. Then Moomintroll and the Snork Maiden disappear, and the family realize that the house may hold the answers to more than they ever dreamed.