Dr. Tucia Hatherley is a licensed physician who abandoned her medical practice after enduring a traumatic internship under an abusive supervisor. She struggles with post-traumatic stress and compulsive hair-pulling, isolating herself while trying to provide for her young son. Facing insurmountable debt and the threat of an asylum for her child, she makes the desperate choice to join a traveling medicine show.

Huey Horn operates "The Amazing Adolphus Show," peddling a fraudulent rattlesnake oil elixir to unsuspecting crowds. He uses charm and theatrics to mask his deeply manipulative nature. He specifically targets vulnerable individuals with troubled pasts, using blackmail and debt manipulation to keep them trapped in his employment.

Darl is a handyman for the medicine show who manages the wagons and performs repairs, intentionally staying out of the spotlight. He has a badly repaired cleft lip and keeps his background guarded. He shares a long history with Huey that prevents him from leaving the troupe.

Fanny performs as "Grazyna the Dancing Giant" in the medicine show, utilizing her background as a trained ballerina. Her gigantism makes her a target for spectacle, but she maintains a warm and empathetic personality. She quickly steps in to help Tucia manage the severe anxiety of performing onstage.

Cal is a highly skilled musician who performs under the degrading stage name "Cal Crip Caboo." His legs bow outward due to untreated childhood rickets. Despite the cruelty of the crowds, he consistently commands their attention through his immense musical talent.

Toby is Tucia's seven-year-old son who has Down syndrome. He requires steady routine and care, which proves difficult for his mother to secure while working. He possesses a gentle, innocent disposition and quickly bonds with the animals and children he meets on the road.

Lawrence is a young Indigenous American man whom Huey forces to perform under the caricature of "Chief Big Sky." He speaks perfect English but is commanded to act otherwise for the audience's entertainment. He channels his frustrations into a leather-bound notebook where he writes poetry and sketches.

Al is a young boy traveling with the Trouts, slightly older than Toby. He adapts easily to the unconventional life of the traveling medicine show and provides Toby with his first real friend.

Dr. Addams is a renowned and powerful surgeon who oversaw Tucia's medical internship. He uses his prestige to manipulate and abuse female subordinates. His actions destroyed Tucia's career and left her with lasting trauma.

Kit is a monkey originally purchased by Huey to serve as another performing act for the crowds. The animal vehemently rejects Huey's control and instead attaches itself to Toby, becoming a source of comfort for the boy.

Mrs. Harsnatch is the hired babysitter Tucia pays to watch Toby while she works at the clothing factory in St. Louis. She is negligent in her duties, often ignoring the boy to sleep or read the newspaper.