Dr. Marina Singh is a pharmacologist in her early 40s working for the Vogel Corporation. Formerly a promising obstetrician at Johns Hopkins, she abandoned clinical medicine for lab research following a traumatic surgical accident. Haunted by childhood memories of her father abandoning her family, she suffers from severe nightmares triggered by the anti-malarial drug Lariam. She is fiercely loyal and empathetic, traits that push her to travel to the Amazon to investigate her friend's fate.

Dr. Annick Swenson is a legendary 73-year-old biomedical researcher leading an Amazonian research station funded by Vogel. She is notoriously demanding, fiercely protective of her work, and deliberately cuts off communication with her corporate benefactors. Having spent nearly 50 years studying the remote Lakashi tribe, she commands intense loyalty from her staff but instills deep apprehension in her former students.

Mr. Jim Fox is the 61-year-old CEO of the Vogel Corporation and the first to hold the position without formal medical training. A calculated businessman, he is responsible for funding Dr. Swenson's fertility research and extracting a return on that investment. He carries guilt over sending Anders to the Amazon, a decision driven by his desire to keep his covert relationship with Marina hidden in Minnesota.

Easter is a deaf, undersized twelve-year-old Amazonian boy adopted by Dr. Swenson. Highly intelligent and remarkably capable, he serves as the primary boat pilot for the research station, steering through the winding Amazon River with ease. He possesses a sweet disposition and an easy charm that bridges cultural and linguistic gaps.

Dr. Anders Eckman is a good-natured, midwestern pharmacologist and father of three. He travels to the Amazon on behalf of the Vogel Corporation to check on Dr. Swenson's progress but is entirely ill-equipped for the extreme heat and hazards of the rainforest. The vague details surrounding his reported death set the novel's central investigation in motion.

Karen is Anders' wife and the mother of their three young boys. Devastated and bewildered by the vague circumstances surrounding her husband's reported death, she suffers from severe insomnia and grief. Desperate for answers but unable to leave her children, she implores Marina to travel to Brazil in her place.

Milton is a smart, street-savvy Brazilian man hired by the Vogel Corporation to serve as Marina's guide and translator. Resourceful and highly capable, he helps Marina survive the chaotic streets of Manaus and supplies her with basic necessities. He acts as a stabilizing force during her disorienting transition into the Amazon basin.

Barbara is a tall, tanned, and fashionably dressed Australian expatriate who lives in Dr. Swenson's Manaus apartment. She claims to be a writer but primarily functions as a gatekeeper for Dr. Swenson, deliberately delaying anyone seeking access to the Amazonian research station. She enjoys a carefree, bohemian lifestyle funded entirely by Vogel.

Jackie is a laid-back professional surfer from Australia. He assists his wife in minding Dr. Swenson's affairs in Manaus, enjoying a rent-free lifestyle while keeping corporate visitors distracted. He struggles with chronic carsickness but maintains a friendly, frivolous demeanor.

Dr. Martin Rapp is a famous, deceased Harvard ethnobotanist who led the initial 1960 expedition to the Lakashi tribe. He serves as a legendary figure in the botanical community, known for his effortless brilliance as well as his intense self-absorption during research missions. His legacy deeply influences the current generation of scientists at the station.

Alan Saturn is an American botanist stationed in the Amazon. He idolizes his former Harvard professor, Dr. Rapp, and passionately defends his legacy against criticism. He is responsible for making regular boat runs to the Jinta trading post to collect mail and supplies.

Nancy Saturn is an American botanist who shares a tense dynamic with her husband regarding the legacy of their academic predecessors. She takes a highly critical view of past researchers' ethics and helps maintain the strict secrecy surrounding the local ecosystem and the station's botanical discoveries.

Dr. Budi is an Indonesian researcher managing clinical organizations for Dr. Swenson's team. He acts as a stabilizing presence among the scientific staff, occasionally stepping in to mediate tense conflicts between researchers and corporate visitors.

Dr. Thomas Nkomo is a Senegalese research physician who possesses a strong aptitude for languages, having mastered the local Lakashi dialect. He is polite and welcoming, though he remains evasive when questioned about Anders' final days at the camp.

Benoit is a mission-educated Jinta tribesman working at the research station. Fluent in Portuguese, he harbors ambitions to become a prominent river tour guide. This desire for professional recognition sometimes leads him to take reckless risks to impress foreign visitors.

Rodrigo operates a local outfitting store where the Vogel Corporation maintains an account. He serves as the chief supplier for Dr. Swenson's remote research station, providing necessary goods and occasional information about the elusive scientist's movements through the city.

Josh is a physician and Marina's ex-husband. Their short-lived marriage occurred during their demanding medical residencies at Johns Hopkins and ultimately dissolved under the immense pressures of their medical careers.

Mary is Mr. Fox's deceased wife and the mother of their two daughters. Her premature death from lymphoma left a lasting impact on her husband, shaping his cautious approach to subsequent relationships and his fear of losing another partner.