Lucy is a 12-year-old girl with red hair and freckles living in the coastal town of Rockport, Massachusetts. She considers herself an artist rather than a scientist, preferring to sketch specimens while working on school projects. When a local fisherman brings in a great white shark, the event surfaces unresolved emotions surrounding her mother, a late marine biologist. Lucy relies heavily on her childhood companion as she enters adolescence and begins confronting her lingering grief.

Fred is a 12-year-old boy who lives next door to the Everhart family. He manages asthma with a frequent use of his inhaler. He spends much of his free time listening to jazz music, especially albums by Miles Davis. Naturally curious about the natural world, he takes the lead on a science field guide project and actively encourages his neighbor to research marine biology.

Tom works as a Rockport police detective and a scuba rescue diver. He also spends time as an amateur photographer, capturing local scenes in a darkroom. Following the sudden loss of his wife five years earlier, he has withdrawn emotionally, often taking demanding underwater assignments to avoid sitting with uncomfortable feelings. He struggles to manage household duties like cooking while maintaining his demanding professional schedule.

Helen was a brave, outgoing state marine biologist who studied the habits of great white sharks off the coast of Cape Cod. She passed away from a sudden brain aneurysm five years before the current events, leaving behind a legacy of comprehensive research proposals. In life, she acted as the social center for her family, effortlessly connecting people and encouraging environmental conservation.

Sookie is a sun-bleached, fourth-generation Rockport fisherman who operates his own commercial boat. He attended high school with Lucy's parents but has distanced himself from the family over the last five years, preferring isolation over confronting painful memories. He acts stubbornly at times but possesses deep loyalty to the people he cares about.

Mr. Patterson is the elderly next-door neighbor of the Everharts. A widower for twenty years, he spends his days sitting in a rocking chair on his porch, listening to sports radio broadcasts. He acts as a quiet, observant surrogate grandfather to the neighborhood children and provides steady companionship to the families on his street.

Vern is an older, semi-retired marine biologist living in Maine. He previously mentored other state researchers and maintains a passionate interest in ocean ecosystems despite experiencing short-term memory loss. He relies on an at-home nurse for daily care but remains eager to discuss science and share photographs from his career.

Fiona is an older teenager with an artistic aesthetic characterized by short black hair and vintage style choices. She projects strong self-assurance regarding body image and womanhood, frequently countering unrealistic media representations. She acts as an older mentor to the younger neighborhood girls, taking them shopping and offering advice on entering adolescence.

Maggie is a single mother raising three children in the house next door to the Everharts. She monitors her children closely, sometimes requiring her older daughters to supervise their younger brother to keep him out of trouble. She tries to provide practical support to her neighbors by cooking meals and checking in on them.

Dr. Robin Walker is a professional biologist working in Massachusetts. She aims to revive historical research projects concerning great white sharks along the Cape Cod coast, continuing the academic efforts of her predecessors. She encourages civilian interest in marine biology.

Bridget is a local teenager who helps look after her younger brother. She participates in typical high school social activities, including attending local parties, and casually helps younger neighbors feel more mature by offering to do their makeup.

Marion is a professional at-home nurse working in Maine. She manages the daily health requirements of her elderly patient, offering practical medical advice while safely facilitating his social visits and research discussions.

Lester is an older teenage boy living in Rockport. He hangs around local spots like the quarries and the docks, representing the older, more unsupervised crowd of young adults in the coastal town.

Mr. Scanlon is a counselor working at the local middle school. He provides a supportive ear for students processing complicated emotions and uses casual games like gin rummy to make conversation feel less intimidating.

Ms. Solomon is a middle school science teacher who assigns extra-credit field guides. She encourages students to blend art and science, validating different learning styles and pushing them to observe the natural world closely.