Fredrik Welin, a 66-year-old retired surgeon, lives alone on a small island in the Swedish archipelago, inherited from his grandparents. His only companions are an elderly cat and a nearly deaf dog. Each winter morning, he cuts a hole in the ice and plunges into the freezing water to confirm he is still alive. His sole regular human contact is Jansson, the archipelago postman, a persistent hypochondriac who treats Fredrik as his personal physician. In the living room, a large anthill has been growing for years, slowly consuming a tablecloth on the dining table. Fredrik grew up poor and became a surgeon, but 12 years ago a catastrophe ended his career and drove him to the island. He believes nothing will ever change. He is wrong.
In early January, a woman appears on the ice, leaning on a wheeled walker. Fredrik recognizes Harriet Hörnfeldt, the woman he loved and abandoned nearly 40 years earlier. In 1966, they were deeply involved in Stockholm, but when Fredrik received a scholarship to study in the United States, he left a day early without saying goodbye and never contacted her again. Harriet collapses on the ice, and Fredrik wheels her to the house. That night, searching her handbag, he finds a letter revealing she has terminal stomach cancer.
Harriet asks Fredrik to fulfill a promise he made before he vanished: to take her to a remote forest pool in northern Sweden where his father once swam. They set out northward. At an inn, Harriet wakes screaming from a nightmare and punches him in the face. He confesses he found the letter about her illness. She demands to know why he abandoned her, accuses him of lying his way through life, and he offers no real explanation.
They reach the pool, now frozen. Fredrik digs a path so Harriet can walk to the center with her walker. As they stand in silence, Harriet expresses regret at tracking him down, saying the pain he caused "sent me to hell and back" (71). Fredrik steps onto a dark patch, falls through thin ice, and nearly drowns. Despite her frailty, Harriet pushes her walker to the edge so he can grab a wheel and pulls him out.
Instead of heading home, Harriet redirects their journey eastward to meet her daughter, who lives in a caravan in the forest. A woman emerges in a pink dressing gown and high-heeled shoes. Harriet introduces her as Louise, then tells Louise that Fredrik is her father. Louise, now 37, was conceived shortly before Fredrik abandoned Harriet, who discovered the pregnancy after he vanished. Louise had been told her father was a man who went to America to research bees.
Fredrik begins to know his daughter. Among Louise's eccentric neighbors is Giaconelli Mateotti, a 90-year-old Italian master shoemaker who left Rome for the silence of the Swedish forest. Giaconelli measures Fredrik's feet with meticulous precision, and Louise announces the shoes will be her gift to her father. When Harriet must be hospitalized, father and daughter talk through the night. Louise describes her obsession with the painter Caravaggio, whose works she has traveled across Europe to see. Fredrik confesses the catastrophe that ended his career: He amputated the wrong arm of a 20-year-old competitive swimmer named Agnes Klarström.
Harriet and Louise confront Fredrik about his emotional detachment and his failure to show joy at having a daughter. He storms out and drives home. On his island, he resolves to find Agnes, the woman whose arm he wrongly amputated. A winter of letters follows as he writes to Harriet, Louise, and Agnes. His morning ice baths grow less frequent: Meeting Harriet and Louise has diminished his need to shock himself into feeling alive.
Fredrik drives to Agnes's farm near Flen. A girl named Sima, a teenage refugee from Iran, charges at him with a samurai sword, but Agnes stops her. Recognizable by her empty sleeve pinned to her shoulder, Agnes runs a foster home for at-risk teenage girls. She tells Fredrik she once dreamed of killing him but that hatred is "nothing more than an all-consuming parasite" (141). She squeezes his hand and says the girls are all that matter now.
Fredrik's dog dies in April, and he buries it under the apple tree. Soon after, Sima arrives at the island in a stolen motorboat. Fredrik lets her stay, but the next morning he finds her covered in blood, having cut herself with a fish knife. He calls the coastguard. At the hospital, Sima's condition stabilizes and Agnes arrives to sit with her. Overnight, sudden internal bleeding occurs, and Sima dies without regaining consciousness. On the quay, Fredrik tells the taxi driver, "My daughter has just died," a slip revealing how deeply he felt connected to her.
Weeks later, Louise and Harriet arrive unannounced, Louise's caravan towed by Jansson on an old cow ferry. Harriet, now skeletal, asks to lie in the room with the anthill and listen to the sea. At Harriet's request, they hold a midsummer party. Harriet tells Fredrik she regrets keeping Louise from him as revenge for his abandonment. Jansson stuns everyone by singing "Ave Maria" in a powerful baritone no one knew he possessed.
As her condition worsens, Harriet tells Fredrik she never loved or hated anyone as much as him. She dies at dawn on 22 August. Fredrik and Louise wrap her body in a tar-soaked tarpaulin, place it in the old beached boat, and set it alight. Louise buries the ashes under the apple tree, then departs in a taxi to visit the endangered cave paintings at Lascaux in France and see Caravaggio's works, leaving her caravan and a promise to return.
Agnes visits the island and reveals her foster home will close because her landlords are evicting her. Fredrik offers to let her bring the girls to his island. That evening, after too much wine, he tries to force himself on Agnes. She fights him off with a kitchen knife. Deeply ashamed, he writes begging forgiveness. She eventually accepts his apology without committing to the move.
A newspaper photograph reveals that Louise staged a naked protest about the cave paintings at a European summit. Fredrik smiles: He has a daughter he can be proud of. Louise returns in December and erupts when she learns of his invitation to Agnes, believing he is giving away her inheritance. "I thought you were going to abandon me again," she says (235). Fredrik assures her the island will always be hers, and they make peace.
On the winter solstice, Fredrik suffers a sharp chest pain, his second episode of angina. Louise departs again, promising to return in spring. Alone, Fredrik receives the shoes from Giaconelli: black with a hint of violet, fitting perfectly. He wears them around the kitchen every day, never outside. In April, he removes the anthill from the living room and discovers inside it a bottle Harriet left behind, containing a photograph of the two of them when young. On the back, she has drawn a map of the island and written: "We came this far." Fredrik carries the anthill to the pasture, walks round the island watching migrating birds, and acknowledges Harriet's words: They came this far, no further, but this far.