Samantha is a fifteen-year-old Chinese American girl who dreams of opening a music conservatory. A tragic fire claims her father's life, and shortly after, she kills her landlord in self-defense. To evade the law, she disguises herself as a boy named "Sammy" and flees west toward California. She is classically trained in the violin and relies heavily on Chinese astrology to understand her dangerous new surroundings.

Annamae is a fifteen-year-old self-emancipated Black girl who joins Samantha on the run. Operating under the male disguise "Andy," she possesses practical survival skills and a profound Christian faith. She travels west with the specific goal of reuniting with her older brother at Harp Falls. Her pragmatic approach to survival balances Samantha's more theoretical education.

West is a skilled teenage cowboy from Texas traveling the trail with his cousin and friend. He handles the difficult riding and roping required for survival. Scars from a troubled, abusive upbringing make him intensely guarded around others. He holds a secret appreciation for art and often acts as a protector when the group faces sudden danger.

Ian and Angus are Scottish brothers who travel with their father's wagon train. Stocky and aggressive, they operate as bullies on the trail. They quickly develop a bitter vendetta against Sammy and Andy after a public humiliation, personifying the pervasive racial hostility that marginalized travelers face.

Ty Yorkshire is a corrupt landlord and hotel owner in St. Joe, Missouri. He attempts to exploit Samantha's sudden tragedy by cornering her in a bathtub and forcing her into sex work. His violent and predatory actions directly trigger the central flight of both young women.

Cayenne is an outgoing cowboy fleeing trouble in Texas. Characterized by sandy curls and green eyes, he contrasts his cousin West's brooding nature with a talkative and joking demeanor. He lacks formal education and sometimes speaks insensitively, but he proves to be a loyal presence within the traveling group.

Peety is a Mexican cowboy who serves as the wrangler for the group's horses. Proud of his mixed European and Aztec heritage, he provides an open-minded perspective on race and relationships that differs from the typical emigrant views on the trail. He is gentle with the animals and quickly becomes a supportive ally to the younger travelers.

Isaac is Annamae's older brother who was separated from her when they were sold to different enslavers. Remembered by his sister as a kind and optimistic figure, he tried to comfort his siblings through the cruelties of enslavement. He represents Annamae's primary motivation for braving the severe conditions of the western territories.

Samantha's father is a kind Chinese immigrant who ran the Whistle general store in Missouri. He dies tragically in a fire at the beginning of the story. He instilled a deep pride of heritage and a love of classical music in his daughter, leaving behind memories that shape her daily decisions.

Mr. Trask is the closest friend of Samantha's father. He recently departed for California with the goal of establishing a music conservatory. He holds a precious jade bracelet that belonged to Samantha's deceased mother, making him the central destination for her cross-country journey.

Mr. MacMartin is the Scottish patriarch leading a wagon train on the trail. Unlike his cruel and vindictive sons, he demonstrates a capacity for shame. He ultimately offers Samantha and Annamae a mule as a formal apology for his sons' violent behavior.

Tommy is Annamae and Isaac's deceased younger brother. He suffered terribly under the harsh realities of enslavement before dying at the age of seven. His memory is kept alive by his siblings through stories and a specific charm worn on Annamae's wrist.

Mrs. Calloway is a traveler connected to the Underground Railroad. Married to the man whose wagon Samantha and Annamae initially hide inside, she possesses strong abolitionist principles. She quickly deduces the girls' true identities and uses her position to offer them brief safety.

Lady Tin-Yin is an Italian-made violin named by Samantha's father. Having been in the family for four generations, the instrument functions as more than a wooden object. Samantha personifies the violin as her closest friend and primary source of emotional stability.

West's father is an abusive man from Texas who struggled with alcohol addiction. He inflicted severe physical and emotional scars on his son during childhood, unable to accept West for who he truly is.

Mr. Calloway is a traveler whose wagon serves as the hiding place for Samantha and Annamae. He interacts with suspicious law enforcement early in the journey, unknowingly acting as a shield for the fugitives hiding in his transport.

Esme is Peety's younger sister who was tragically kidnapped in a market when she was only five years old. Her loss remains a significant emotional wound for Peety.