Teranesia is a 1999 science fiction novel by Greg Egan. The novel follows protagonist Prabir Suresh, who lives on an island in the South Moluccas with his biologist parents, who are investigating the unique evolutionary traits of butterflies on the island. As civil war erupts in Indonesia, Prabir and his baby sister Madhusree must escape the islands. When they grow up, Madhusree becomes a biology student, motivated to carry on her parents' legacy in uncovering the evolutionary phenomenon. Prabir reluctantly follows her, as he must navigate and confront the truth that shaped his past.

The novel encircles notions of sexuality and free will. Where Egan is regarded as a hard science fiction author, Teranesia stands out as one of his few character driven novels. Egan's personal interest in migration politics permeates through Teranesia, as he explores the migration experience of Prabir and Madhusree as they seek asylum in Canada. Teranesia received critical acclaim, as well as award nominations and wins. The novel won the 2000 Ditmar Award for Best Novel but Egan declined to accept the award.

9-year-old Prabir Suresh lives on a small tropical island among the South Moluccas where strange mutations generate unique plants, birds and creatures. His life revolves around the jungle, which he calls Teranesia; school; and friendships he makes on the internet. Prabir lives on the island with his baby sister, Madhusree and parents who are both research biologists, currently studying the evolution of a species of butterflies that strays from conventional evolution.

Civil war breaks out in Indonesia, with heated attacks against the Javanese empire. One day planes fly by and drop mines, some falling in Prabir's family garden. While tending to the garden the next day, Prabir's father is gravely injured by a mine. Prabir and his mother attempt to help pull his father out of the garden, but his mother loses her balance and Prabir witnesses them both die after falling on another mine. Shocked from the explosion and sudden death of his parents, Prabir escapes the island with his fifteen-month-old sister. As the civil war expands across the area, they scramble on a boat to the nearest inhabited island, where they are taken to Australia, and seek asylum with their aunt in Canada, far way away from Teranesia and their family's homeland of India.

Prabir dedicates his life to parenting Madhusree over the next 20 years, while navigating his sexuality as a gay man and being separated from his homeland. He starts work at a bank and Madhusree grows to pursue biology, carrying the lineage of their parents' passion for evolutionary research. One day, reports emerge of an abnormal species of plants and animals that have mutated throughout the South Moluccas region that are going out of control, including on the island Prabir called Teranesia. Prabir recognises the similarity in these characteristics to the butterflies his parents were studying many years ago. Madhusree decides to go on a scientific expedition to explore these strange mutations. Prabir suffers anxiety and apprehension at the thought of revisiting the islands they grew up in. He tries desperately to convince Madhusree not to go, but this only motivates her more strongly. Prabir, left alone, broods about the meaninglessness of his life and attempts suicide. In the last minute, he decides to chase her to the islands instead, still distressed at the thought of her revisiting Teranesia.

Traveling back to the islands, Prabir undergoes a traumatic realisation of his past. When Prabir was young, he exchanged messages with a professor in the United States, posing as his father. While trying to reassure her of the growing unrest, he made statements that made him sound like an insurgent. He assumes the messages were intercepted, and believes he's the reason the militia plane flew to their home, ultimately causing his parents' deaths. In considering his past, Prabir realises his effort to prevent Madhusree from traveling to the islands was more to protect himself than her.

Now invigorated to uncover the mystery of the mutations, Prabir encounters Martha Grant, a biologist who is also studying them. Grant is working under a pharmaceutical company, which forbids her to publish her results. They strike a deal – Prabir will guide her to the island Teranesia if she promises to publish her results on the internet. Grant challenges Prabir, asking if he had ever tried to protect Madhusree for another reason than the fact she's his sister. Prabir becomes agitated at the thought that his inclination to take care of Madhusree was genetically determined rather than a choice he made of his free will.

A research team identifies the gene causing the unusual mutations as the São Paulo protein. A physicist on the team suggests the protein uses quantum superposition to figure out which mutation is most beneficial to the organism. They realise this is how the mutations are propagating at such a rapid pace.