Henry Shackleford, a free (not “freed”) slave living in the Kansas territory in 1856, has a fateful run-in with abolitionist John Brown – who mistakes him for a girl, “frees” him and welcomes him into his ragtag army with the nickname Onion. Quickly awakening to the promise of a better life, Onion dons a dress and hides his identity in plain sight; serving as witness, aide, confidant and solider for John Brown.