Moomin and the Midsummer Mystery - Tove Janssonová

If you haven't met a Moomin yet, you're missing the most magical fun . . .It's a long, lazy midsummer afternoon in Moominvalley and the whole family are relaxing outdoors. But suddenly Moominpappa's precious notebook and fountain pen vanish, and the garden starts to feel unseasonably cold. Can Moomintroll and his friends follow the clues and solve this curious mystery?