In the midst of the Mexican-American War, Brigadier General Stephen Watts Kearny and his troops march into Santa Fe, New Mexico, after defeating the state's militia under Governor Armijo. Kearny establishes a joint civil and military government, appointing Charles Bent as acting civil.

Amidst this turmoil, Kearny encounters a notorious saloon owned by Maria Gertrudis Tules Barceló, commonly known as Doña Tules or La Tules. Despite her negative reputation among Americans and rumors of her ill-gotten fortune, Kearny borrows funds from her to pay his invading troops, which enables them to continue occupying Santa Fe.

Doña Tules is infamous for her gambling skills and is known to play high stakes games of Monte. In one such game, she faces off against a famous card shark and emerges victorious.

However, when he draws his pistol, she beats him to the pull and kills him. Meanwhile, tensions rise in Santa Fe as a conspiracy against the Army is uncovered.

Doña Tules exposes the plot, preventing a potential massacre and solidifying her position as an important figure in the community. As the conflict between the Americans and Mexicans intensifies, Doña Tules finds herself caught up in a large shoot-out in the Santa Fe Plaza.

The outcome of this violent confrontation will determine the fate of both sides. .