Onion and new recruit John Cook head to Harper's Ferry to prepare for the arrival of John Brown and his army. However, Onion quickly struggles to perform his mission of recruiting more African-American soldiers from the area when Cook's reckless behavior threatens their exposure to suspicious neighbors. After several weeks of waiting, Brown, his army and his daughter Annie finally arrive—creating a new distraction for Onion: true love.

The plan to take control of the nation's largest armory at Harper's Ferry is finally put into action. However, a crucial mistake by Onion threatens the success of the entire operation. John Brown's army takes hostages, grabbing the attention of an angry mob and local militia. With shots firing, Onion is sent out to get reinforcements.

John Brown and his remaining army take a last stand as more federal troops descend upon Harper's Ferry. With John Brown captured and held for public execution, Onion, truly on his own, risks his life to say his goodbyes to Brown.