In the middle of the night, the inhabitants of Moominvalley are awakened by distant explosions. At the same time, a pretty young girl appears in the valley, completely exhausted. Snufkin carries her to Moominmamma's house. One of the following nights, when the explosions can be heard from the sea, the Moomins try to get to the bottom of the matter. From the beach, they see a rowboat on the horizon with someone sitting in it who looks very much like Mr. Hemul. But what is Hemul doing in a rowboat at night?