[1] First published in 1965, the novel is set contemporaneously with Moominvalley in November (1970), and is the final installment in the series where the titular Moomin family are present within the narrative.

The book follows the titular Moomin family as they arrive on a deserted island in the middle of the sea, documenting their experiences as they become familiar with their newfound surroundings.

[2] The book's original title is a loose reference to Ernest Hemingway novel The Old Man and the Sea, though this is not reflected in the translation.

Moominpappa becomes dissatisfied with his life in Moominvalley, so he organizes a journey for his family to find a lighthouse in the sea.

Meanwhile, Moominmamma becomes increasingly melancholic as her dream of planting a garden fails, and her longing for home grows stronger.

Slowly, he starts to grow fond of her, and when the lamp ultimately runs out of kerosene, the Groke is no longer cold.