That grandmothers enjoy a special relationship with their grandchildren is both a fact of life and a given of children’s literature. Consider the case of young Sophia, impossibly precocious beyond her six years, who inhabits a tiny island in the Baltic Sea with her grandmother, who, though ailing, is a font of adventure. Sophia’s mother has recently died—another trope of children’s literature—and her father, though glimpsed here and there, remains silent in Tove Jansson’s 1972 novel, The Summer Book, solemnly working (and occasionally drinking) in the background.

Grandmother is nearing the end of her life. Sophia is just at the beginning of hers, but they share many of the same delights and secret places. One is a grove of trees on the edge of their island, exposed to the bitter winds that blow off the cold sea until, falling one by one, they “formed a tangled mass of stubborn resignation.” This place, which they call the “magic forest,” pointedly illustrates the thin line between life and death, where “the balance between survival and extinction was so delicate that even the smallest change was unthinkable.”

Yet change comes. Nearby, a bulldozer grinds away at a living forest, “an enormous, infernal, bright yellow machine that thundered and roared and floundered through the woods with charging jaws.” Across a narrow channel with a broad view of an unspoiled mainland, a rich businessman builds an ostentatious house and, flouting the customs of the island, posts a “No Trespassing” sign. Grandmother, a born anarchist, snorts and breaks into the trophy house, an awed Sophia in tow.

Grandmother is also a born teacher. Sometimes she tires of Sophia, worn out by her endless questioning, but more often she is there with just the right lesson. When Sophia cuts a worm in two, it’s not enough to comfort her: Grandmother suggests instead that Sophia write a book, which Sophia calls A Study of Angleworms That Have Come Apart. When Grandmother ventures editorial changes, Sophia impatiently demands that she not interrupt, for she has come without prompting to the grown-up conclusion that for the two halves of the worm, “life would be quite different, but they didn’t know how.”

Life is different, just so, for Sophia without her mother. It won’t be long, Jansson lets us know, before Grandmother, frequently so tired that she has to rest midwalk, leaves the island, too. Hints abound: When Grandmother faces a dark staircase in the middle of the night, for instance, she notes that “the darkness was absolute.” She isn’t afraid, though, and for all its intimations of mortality, Jansson’s slender novel is joyful, celebrating love, learning, and family.

It’s tempting to think of Tove Jansson (1914-2001) as a grown-up Sophia, full of curiosity and adventure herself. The author of the beloved Moomin children’s book series, she summered with her life partner, the artist Ida Helmi Tuulikki Pietilä, on an island in the Gulf of Finland for many years. There, she wrote short stories, children’s books, a memoir, and several novels, including The Summer Book, available from New York Review Books in an English translation by Thomas Teal. It’s a story ripe with wisdom, resistance, and hope—and great summer reading 50 years on.

Gregory McNamee is a contributing editor.