Blueback takes place during the late 20th century in Longboat Bay, a fictional town on the coast of Western Australia. Abel Jackson is 10 years old. He and his mother, Dora, live off the land and sea in Longboat Bay, which is hard work but also a lot of fun for Abel. He loves to swim in the sea and explore the forest behind his home. To Abel and his mother, the bay is especially important because it holds memories of Abel’s father, a pearl diver who died when Abel was two years old. Abel’s father’s memory lives on especially through a peppermint tree on the Jacksons’ land, which Dora has transformed into a shrine for Abel’s father.
One spring morning, when Abel and his mother go diving for abalone, Abel encounters a huge blue groper underwater. At first, Abel is frightened by the enormous fish, but then he’s amazed by the fish’s beauty. He names the fish Blueback, and he and Blueback quickly become friends. At school, Abel gets in trouble for daydreaming about Blueback. He can’t stop wondering what the old fish thinks about. As the seasons go by, more people learn about Blueback, and Abel worries that someone might spear Blueback to try to win some fame. Abel understands fishing for food, but he can’t comprehend why anybody would kill fish just for fun. Fortunately, Blueback stays safe. However, a different tragedy occurs when Abel is 12 years old. A friendly abalone diver called Mad Macka dies, likely from a heart attack, while diving alone in Longboat Bay.
The next year, Abel leaves Longboat Bay to attend high school in a bigger town farther inland, where he has to stay in a hostel. Abel doesn’t want to be apart from his home or his mother, and throughout the school year he feels homesick and dreams about Blueback. When he finally returns home for the summer holiday, he learns that Mad Macka’s family has left Macka’s boat to him. Abel learns how to sail the boat, exploring the coastline with his mother.
That same summer, a new abalone diver named Costello comes to Longboat Bay. Costello has a bad reputation for stripping reefs bare wherever he dives, so Dora is nervous about his arrival. When Abel sees Costello take an excessive number of abalone and bleeding fish from the bay, Abel resolves to stop Costello himself. Abel sails out to Costello’s boat and saves some of the abalone by returning them to the sea. Then, to his horror, Abel realizes Costello is also trying to spear Blueback. Abel’s mother successfully protects Blueback, and Costello is later fined for overfishing. Costello’s viciousness teaches Abel that greedy humans are capable of great cruelty toward nature.
In the following years, Abel and his mother face more upsetting events. Land developers grow interested in building a resort in Longboat Bay, so they attempt to pressure Dora into selling the Jacksons’ land. Dora doesn’t give in, and eventually the developers leave her alone, but Abel is angry that the selfish businessmen see his beloved home only as a source of money for themselves. Additionally, fish begin to die mysteriously along the coast, and Dora believes that the sea is sick.
Abel goes to university to study the ocean, but he still can’t figure out all the enigmatic ways in which the ocean works. Even when he becomes a marine biologist alongside his wife, Stella, Abel feels like he’s no closer to answering his boyhood questions about the sea. While Abel and Stella travel around the world for their jobs, an oil spill near Longboat Bay almost threatens disaster for Abel’s home. Soon after, Dora experiences a tremendous storm in Longboat Bay, which unearths thousands of whale bones on the beach. The bones are relics from more than a century ago, when the Jacksons first came to Longboat Bay to hunt whales. Seeing the bones leads Dora to conclude that she must give back to the sea—not just take from it—so she starts writing letters to politicians to protect her home. Through her determination and passion, Dora convinces the government to declare Longboat Bay a sanctuary.
As soon as Abel and Stella learn that Longboat Bay has become a protected marine park, they return to Abel’s home to celebrate Dora’s success. However, Dora has grown older and feebler in Abel’s absence, and she falls and breaks her hip. Abel realizes his mother is too old to live on her own. To take care of his mother and remain connected to the place he loves, Abel agrees with Stella to stay in Longboat Bay. Together, Abel and his wife quit their jobs as famous scientists and focus on caring for the land, the sea, and their family.
In the winter, Abel and Stella’s daughter is born. Abel names her Dora after his mother. By now, Abel’s mother is a frail, white-haired woman who can’t walk. She spends her time listening to the ocean, resting, and telling stories. One day, Abel carries his mother to the shore so she can float on the sea in his arms. The next day, she dies peacefully in her sleep, and Abel buries her in the family cemetery behind the orchard.
Abel and his family continue to live happily in Longboat Bay as the sea begins to thrive again. Abel accepts that he may not learn the secrets of the sea in his lifetime, and he contentedly allows the sea to “be itself.” When their daughter turns three years old, Abel and Stella go diving with her. For the first time, little Dora meets Blueback, who is “the colour of all their dreams” and full of life.