Moominsummer Madness — Tove Jansson

A huge wave has crashed through the valley, flooding the Moomins out of their home! With their usual resilience, the Moomins and their friends move into the first house that comes bobbing along. It's strange-looking, like a big cave with curtains hanging on either side. And when the house bumps into dry land and Moomintroll and the Snork Maiden decide to spend the night on shore--then the adventure really begins. Moomintroll and the Snork Maiden get lost, and Moominpappa decides to write a play which they will perform in the house, in the hope that Moomintroll will hear about it and find his way home.
"Moominsummer Madness," the fourth in Tove Jansson's classic series of books about Moominvalley, is enchanting and full of exciting adventures and surprises, some of them odd even by Moomin standards!