Cadence is a responsible nineteen-year-old managing her family's farm while holding onto aspirations of a publishing career in New York City. She works at a private beach club to earn money and writes a local newspaper column called "Up-Island Happenings." She co-founds a reading group to bring literature to the community. She regularly sacrifices her own career opportunities to maintain stability for her younger sister and aging grandmother.

Briar is a sixteen-year-old girl who closely tracks local military activity and reports suspected submarine sightings to dismissive authorities. She dresses in men's clothing, builds identification models at the Van Ryper Model Company, and deeply distrusts official narratives. She searches medicine cabinets for clues and uses a shortwave radio to monitor the coastline. Her habit of investigating restricted areas often puts her at odds with local law enforcement.

Bess abandons her wealthy upbringing in Edgartown to live at the rustic Copper Pond Farm. She despises the affluent club members she serves at work and prefers the unpretentious environment of the Smith household. She helps establish a local reading group and finds a deep sense of belonging with her chosen family, wholly rejecting her mother's elitist expectations.

Marigold is a thirty-four-year-old woman seeking direction following the sudden death of her mother. She arranges a private painting lesson on Martha's Vineyard to escape her unfulfilling life and inattentive boyfriend in California. She wears her mother's gold heart bracelet and quickly finds an unexpected sense of comfort in the island community.

Peter is a German-born man who claims to have defected from military service to escape the current regime. Found unconscious by Briar, his sudden presence forces the local residents into a dangerous legal and moral situation. He possesses medical knowledge and an intense desire to survive, using his skills to prove his value to the household.

Major Gilbert commands the troops training for combat on Martha's Vineyard. Having previously escaped a prisoner-of-war camp, he focuses strictly on military readiness and initially clashes with locals regarding property rights. He gradually softens his rigid approach when interacting with the island residents.

Tom is the older brother of Cadence and Briar who joined the Army after the attack on Pearl Harbor. He plants a vital crop of Burbank potatoes on the family farm to provide for his relatives before deploying. He joins a dangerous military regiment, leaving a heavy emotional void in the household.

Gram relies on a firm Christian faith and practical skills to raise her three grandchildren. She bakes pies for the visiting soldiers, manages the household despite her failing health, and uses oolong tea leaves to predict the future. She serves as the practical core of the family.

Tyson stays in his grandfather's luxurious second home in Vineyard Haven while serving in the military. He maintains an arrogant demeanor, frequently accompanies his socially focused girlfriend, and reacts aggressively to questions about his family's background and private possessions.

Conrad is an older German immigrant living next to Copper Pond Farm. He shares a friendly relationship with Briar, discussing war strategy and accepting small gifts like a miniature tugboat from her. His background invites local suspicion.

Shelby is a young woman whose father works for Ford Motors in Detroit. She enjoys the island's affluent social scene and dismisses the severity of the local wartime conditions.

Winnie stands out from the other wealthy club members through her genuine generosity and lack of pretension. She reads extensively, shares her magazines with the service staff, and actively leverages her professional connections to help local workers find career opportunities in publishing.

Captain McManus heads the local FBI office and enforces rigid, often discriminatory policies on the island. He treats teenage residents with deep condescension while arresting innocent people based entirely on their ethnic backgrounds, representing a paranoid local authority.

Margaret is a twenty-one-year-old member of the island's Portuguese fishing community. She brings a formal, high-minded view to the reading group but quickly proves to be a loyal and essential part of the women's inner circle.

Lydia is Bess's wealthy mother who lives in Edgartown. She constantly disparages the farm residents and uses her financial leverage to try and force Bess back into high society.

Sandra is the eighty-year-old owner of a war memorabilia shop. She treats her epilepsy with coffee and medication, and she maintains a brisk but trusting relationship with the younger locals.

Elizabeth is a highly acclaimed, ninety-year-old painter living on Martha's Vineyard. Despite her reputation as a private person, she agrees to give Marigold a painting lesson and begins narrating a complex historical story.

Nancy is Marigold's recently deceased mother who lived in Los Angeles. Her sudden death from a brain aneurysm leaves her daughter untethered and searching for meaning.

Ronan is a friendly employee at a local bike shop in 2016. He paints in his spare time and quickly establishes a flirtatious rapport with Marigold.

Celia is an educated publishing professional who works for G. P. Putnam's Sons in New York. She is impressed by Cadence's literary knowledge and tries to recruit her.

Dolores is a publishing professional from New York visiting Martha's Vineyard. She helps evaluate the prototype for the special-sized books meant for soldiers.

Mr. Wespi is the severe manager of the Bay Club. He frequently assigns punitive tasks, keeping his employees from pursuing their own opportunities.

Mr. Reed is a relatively relaxed boss who allows his employees access to classified materials for their work. He defends his staff against the heavy-handed tactics of the local FBI.

Amelia is a journalist for the BBC. She shares a history with the military officers on the island and views the local women with clear disdain.

Private Jeffers is an American soldier participating in the local operations. He looks forward to the homemade pies promised by the local community.

Jerry is a thirty-year-old model builder who is training for a local FBI position. He mocks his coworkers and actively tries to catch them breaking rules.

Bert is an Italian American barber on the island who becomes a victim of wartime paranoia. Authorities unjustly detain him simply because of his ethnic background.