Beau Maverick crashes a party in Virginia City thrown by eccentric socialite Kiz Bouchet. Kiz has a penchant for smoking cigars, playing poker, and fighting fires. Recognizing Beau as a fellow free spirit, she hires him to protect her. She believes her life is in danger. Beau discovers that Kiz's cousin Melissa, along with family doctor Pittman and attorney Hanford, are plotting to have Kiz judged incompent so they can split her $2 million inheritance. Beau comes up with a scheme to turn the tables on Melissa.

The Fenians, an Irish Revolutionary Brotherhood, are trained soldiers sworn to free Ireland from British rule. The Fenians have gathered in Dakota City to plan a march into Canada where they want to take hold of a small part of British property hostage in exchange for Ireland's freedom. After England pressures the United States to intervene, Beau Maverick is blackmailed into infiltrating the Fenians ranks by a shrewd Army colonel.