شاب من العبيد في منطقة كنساس عام 1856، يتقابل صدفة مع المطالب بإلغاء الرق جون براون، والذي يقوم بتحريره، حيث يلقب نفسه "أونيون" ثم ينضم إلى جيشه من محرري العبيد.

Following the battle in Pikesville, John Brown, now one of the most wanted men in America, travels north with Onion to raise funds for the abolitionist cause. They take refuge at the home of famed orator and “King of the Negroes” Frederick Douglass and his two wives. When Brown and Douglass clash over methodology, Onion discovers just how complex the fight for justice and human equality really is.

John and Onion continue their fundraising mission, this time heading to Canada on foot. After seeing true freedom for the first time and frustrated with Brown’s increasingly irrational behavior, Onion demands freedom from Brown’s army. But, when the legendary Harriet Tubman endorses Brown in a room full of new recruits, Onion realizes that he may be more invested in the cause and the "old man" than he thought.

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. Series finale.