Sid is an African American bass player from Baltimore whose lighter complexion occasionally allows him to pass as white. He serves as a medical transcriptionist later in life but spends his youth trying to secure a place in the jazz industry. Though competent musically, he struggles with deep-seated insecurities regarding his more naturally gifted peers.

Chip is a talented African American jazz drummer from Baltimore and Sid's closest companion. Unlike Sid, Chip's darker skin makes him a frequent target of prejudice in both the United States and Europe. He covers his deeper emotions with a confident, joking exterior and remains in the music industry well after the war.

Hiero is a nineteen-year-old German-born Mischling of mixed African and European parentage and a trumpet player of rare genius. His mixed heritage makes him a target of intense prejudice under the Nazi regime, leaving him constantly vulnerable. He relies on Sid to translate English for him and approaches his music with intense dedication.

Delilah is a determined Canadian jazz singer who acts as a representative for Louis Armstrong. She presents a sassy, tough exterior but battles inward insecurities regarding her stress-induced baldness. She is fiercely loyal to the band and determined to secure their safety and musical success in Paris.

Ernst is the manager and clarinet player for the Hot-Time Swingers, born to a wealthy German industrialist family. He leverages his considerable resources and family connections to protect his bandmates from the Nazi regime. He serves as a voice of reason for the group, willing to sacrifice his own comfort for the safety of his friends.

Based on the historical jazz figure, Louis Armstrong is a famous trumpeter who serves as a mentor to the younger musicians. He uses his influence to arrange recording sessions and views jazz as a medium for subtle political resistance. He offers profound personal advice that transcends musical instruction.

Fritz is the German alto saxophonist for the Hot-Time Swingers. He is a large, gentle man who remains dangerously complacent about the rising threat of the Nazi regime. He downplays the urgency of fleeing Germany and later accepts a position in a state-sanctioned musical group, creating a severe philosophical divide between him and his former bandmates.

Paul is the Jewish pianist for the Hot-Time Swingers, described as a debonair ladies' man. Because he does not outwardly fit Nazi stereotypes, he passes unnoticed until recognized by name. He is the original source of the band's connection to Hiero and brings a vital energy to the group.

Bill Coleman is a famous American trumpet player working in Paris. He interacts with the Hot-Time Swingers and intends to stay in France despite the advancing war, occasionally collaborating with them on their secret recordings.

Panther Brownstone is a club owner and musician in Baltimore who provides Chip and Sid with their first exposure to the professional jazz world. He hires Chip for a regular gig until discovering his young age, shaping their early understanding of the music industry.

Von Haselberg is a wealthy German industrialist and Ernst's father. He embodies the bigoted, aristocratic snobbery of the era and prefers classical German composers over jazz, yet he agrees to use his influence to secure identity papers for his son's bandmates.

Liesl is Ernst's sister, a wheelchair-bound woman who contracted polio. She resides at the von Haselberg estate in Hamburg and provides a brief moment of friendly interaction for the weary band members.

Tante Cecile is an elderly, senile woman living in Baltimore during Chip and Sid's youth. Chip takes advantage of her poor memory by pretending he and Sid are her deceased sons in order to get treats from her.

Dame Delilah is a stray cat that wanders into the club where the Hot-Time Swingers hide from the authorities. Chip jokingly names the wiry creature after the singer Delilah Brown. The animal provides brief levity for the musicians during a stressful period.