Matilda is a 14-year-old girl living in Philadelphia who dreams of escaping her daily chores to become a successful businesswoman. She works at her family's coffeehouse but chafes under her mother's strict expectations and yearns for independence. The onset of the yellow fever epidemic forces her to mature rapidly and assume responsibilities she previously avoided.

Lucille is Matilda's demanding, hardworking mother who runs the Cook coffeehouse alone following her husband's fatal accident. She comes from a wealthy family but was disowned after marrying a tradesman. The stress of managing the business has left her rigid and highly critical, though she harbors deep, unspoken affection for her daughter.

Captain Cook is Matilda's paternal grandfather and a former Army captain who proudly served under General George Washington during the Revolutionary War. He is a jovial, outgoing man who treats daily life as a military campaign. He provides a gentle, encouraging contrast to Lucille's strict parenting.

Eliza is the talented cook at the Cook family coffeehouse. Born into slavery, she gained her freedom through her husband's hard work, though he died before she could purchase his freedom in return. She is an active member of the Free African Society and a stabilizing, compassionate figure in Matilda's life.

Nathaniel is an apprentice to the prominent artist Charles Willson Peale. He is a cheerful and observant young man who respects Matilda's independent streak. Lucille Cook disapproves of his profession, viewing him as a poor match for her daughter.

Nell is a small, blonde toddler left orphaned by the yellow fever epidemic. Her vulnerability requires immediate attention, forcing those around her to step up as caretakers.

Joseph is Eliza's brother and a skilled barrel maker. He struggles with the illness while trying to maintain a safe environment for his twin boys following the loss of his wife.

Mother Smith is an elderly, highly respected member of the Free African Society. She is practical and unsentimental, dispensing straightforward advice about survival and caregiving during the crisis.

Mrs. Flagg is a large, capable nurse at the Bush Hill hospital. She favors the restorative methods used by French doctors over the harsh bleeding techniques of American physicians.

Polly is a serving girl at the Cook coffeehouse and a childhood friend of Matilda's. Her sudden, severe illness acts as an early warning of the deadly epidemic reaching their neighborhood.

Pernilla is a wealthy, snobbish Philadelphia socialite. She frequently complains about the lack of high-class entertainment during the hot summer and looks down on tradespeople.

Jeannine is the haughty daughter of Pernilla Ogilvie. She openly insults the Cook family's business by calling it a "grog shop" and acts with a strong sense of entitlement.

Colette is Pernilla Ogilvie's recently engaged daughter. Her sudden collapse during the social gathering brings the reality of the fever directly into their privileged lives.

Mrs. Bowles is a straight-backed woman with kind eyes who works as a caretaker for an orphanage. She recruits healthy individuals to help manage the growing crisis.

Robert is one of Joseph's twin sons. Like many young children in the city, he requires constant adult supervision to survive the outbreak.

William is Joseph's other twin son. He becomes dependent on the adults around him when illness threatens his immediate family.

Dr. Kerr is an educated Scottish physician who follows the traditional medical practices of the time, prescribing aggressive treatments such as bloodletting and purging to combat the fever.

Mr. Brown runs the local print shop and publishes the Federal Gazette. He remains in the city to print official notices, mayoral orders, and health advisories despite the growing danger.

Silas is the Cook family's resourceful pet cat. He provides a sense of normalcy and comfort amidst the growing chaos in the city.

King George is a scraggly parrot won by Captain Cook in a card game. He provides background noise in the coffeehouse by mimicking the phrases of its patrons.