While attending school in Madrid (and receiving fencing lessons on the side), Tessa Alvarado learns of her father's death and leaves immediately for her hacienda in California. Upon arriving, she discovers her father had been murdered and the peons starving because of the policies of the local tyrant with the connivance of the wealthy landowners. In a dream, she is visited by the ghost of her father who encourages her to seek justice for the oppressed and avenge his death. Through her servant's tarot cards, Tessa discovers it is her fate to use her skill as a fencer ...
The Queen of Swords is shot while investigating reports that her villagers are being abducted and men sent to Colonel Montoya's prison are never seen again. In spite of her wound, she continues her search and discovers the men being forced to labor as slaves in Montoya's secret gold mine.
An epidemic strikes Tessa's village and the surrounding countryside. When Colonel Montoya is stricken by the fever, Captain Grisham takes advantage of the situation by stealing or destroying Dr. Helm's entire supply of medicine, and blames the Queen of Swords for the theft. Tessa turns the tables on the officer by drugging his drink with herbs that cause fever-like symptoms and, as the Queen of Swords, follows the Captain where he hid the stolen pills.
When Don Aguilera is shot, his son assumes the would-be assassin is Don Fuentes since he recently had a violent argument with the young man's father. The Queen of Swords intercepts the assassin sneaking into Dr. Helm's surgery and discovers the intended victim was the doctor, not the don. While Dr. Helm is spurning the Queen's offer of help, the would-be assassin strikes a deal with Colonel Montoya to help each other rid themselves of their adversaries.
While attending a party, Tessa sees the shadows of two people arguing behind an upstairs curtain, followed by a gunshot and the body of Carmina falling to the ground below. Grisham arrests Anton Rose for the murder of his girlfriend based on Tessa's account. Carmina's brothers demand that Tessa testify that she saw Anton shoot their sister. Anton's mother, the swashbuckling Mary Rose, threatens to kill Tessa if she does. Col. Montoya hopes that Tessa testifies and Mary carries out her murderous threat so he can arrest Mary for murder and seize both her and Tessa's ...
An outlaw gang preys on the dons, preventing their taxes from being delivered to Colonel Montoya, who then confiscates their lands. The ranchers, led by Don Selvera, threaten to have Montoya recalled if they cannot capture the criminals, but Montoya gets the upper hand when he learns that Selvera's spoiled children are the gang's ringleaders.
While trying to protect a deserter who offered to name her father's murderers, Tessa is forced to reveal the hiding place of a young Indian shaman trying to retrieve a gold mask stolen from his father's burial site. The Queen of Swords manages to rescue both men, but the deserter decides it would be more profitable to reveal the Queen's identity to Colonel Montoya rather than provide Tessa with the information she has already paid for.
Montoya and Grisham capture a Queen of Sword impostor after she stole an army payroll. Montoya sees an opportunity to blame the real queen for the heist and convinces the counterfeit swordswoman to continue her robberies so he can obtain additional troops from the Viceroy while driving a wedge between the peasants and the real Queen.
The Queen of Swords rescues the son of a don from a bandit leader known as The Serpent, severely wounding him in the process. The Queen is none too pleased to learn that Dr. Helm has treated his wounds and becomes angrier still when The Serpent's outlaw gang destroys a poor peasant village.
While Montoya and his garrison are in Monterey to meet the new viceroy, Krane, one of Grisham's old associates, returns to exact revenge for testifying against him at his court martial. Krane forces the captain of the guard to help him take over the town by locking up the remaining soldiers and holding the dons hostage. The Queen of Swords organizes the dons's wives to rescue their husbands and rout the Krane's outlaws.
Marta's former lover, Leonardo, visits Southern California in search of his paramour. Leonardo and Marta are arrested when they are found in the company of the sailor's companion who robbed a rancher and killed a soldier attempting to escape. Montoya guarantees his prisoners' freedom if Leonardo will kill a troublesome don who is leading the fight against the governor's planned tax increase.