Moominpappa has committed to writing a great novel about the sea, so the whole family moves to a desolate island where he becomes the lighthouse keeper. It soon becomes apparent that there are a few problems with the island: it's haunted, there's nowhere to enjoy a good cup of tea, and the rat family living in the transistor radio has strictly forbidden the Moomins from using it.

The whole family can enjoy Jansson's satire on true concerns about future things.