Colonel Nathaniel Lyon grows suspicious when Governor Jackson calls out the Missouri state militia, allegedly to train for home defense, and disguises himself as a farm woman to spy on the militia's camp.

Concluding that Jackson intends to use the militia to seize the arsenal for the Confederacy, Lyon gathers his command of about seven thousand men and starts on a six mile journey toward “Camp Jackson”, arriving from several directions and surrounding the camp.

Lyon demands and receives the camp's unconditional surrender.

When he parades his eight hundred prisoners through St. Louis, a riot breaks out in the city, which remains on the edge of chaos with violence erupting sporadically.

Lyon is officially promoted to brigadier general on May 17.