In 1848 in an auditorium of police officers, criminal investigator Quentin Cook is displaying how science can be used to investigate crimes; by using fingerprinting, a magnifying glass and drawing conclusions from evidence. Afterwards, Quentin meets his fiance Clarissa who wants to marry him.
At the Capitol Bank and Trust in New York, bank president Ashe is standing in front of a map of Mexico, telling Tyler Jackson the importance of acquiring certain tracts of land in Mexico where a railroad will be built. The land must be acquired within 90 days or the railroad will be built elsewhere.
In the Mexican town of Santa Rita, Maria Alvarez is playing Connect with her horse while her father Pedro is inside the bank asking why the bank sold his mortgage to a US bank. The banker Bernardo tell him that the owner of bank don Diego had no option. Maria is sitting outside the bank when seven grim looking men enter the town by horse. When Pedro leave the bank, he is very concerned but Maria promises to speak with don Diego immediately.
Tyler Jackson enters don Diego's office, looking at the photos on the wall displaying photos of don Diego's daughter Sara growing up. Sara herself is outside in the courtyard training her horse. When don Diego enters he offers Jackson a drink and tell him that Sara is the spitting image of her deceased mother and that Sara has spent the last 10 years in Europe. When she enters her father's office, don Diego tell her that Jackson's bank has offered to provide much needed capital to his bank. She expresses surprise that a US bank would have any interest in a small rural Mexican one. Jackson's request to have dinner with her is politely rejected.
Maria is denied entry to don Diego's house by Jackson's men at the front gate but instead she enters the house from the back. Outside don Diego's office, Maria meet Sara very shortly before don Diego's men capture her. While she is dragged through the house she is screaming that don Diego is a traitor for selling her father's land. Meanwhile don Diego signs a contract with the US bank. They toast to the future.
Later, Jackson and his men go to the Alvarez farm to tell him that his loans have been foreclosed and that the bank is taking over the farm in exchange for 1 peso. "Over my dead body" say Pedro before Jackson shoot him down. Jackson give him a receipt before burning the house.
Maria is released by the sheriff. When she returns home she finds her father badly injured. Sara is visiting an old friend who has helped her with her horse. When Jackson and his men show up, they explain that his farm has been foreclosed. When he protests he is shot down. Sara ride away from there quickly on her horse. When she returns home she find her father dead in his office. Jackson is there and explains that her father had a fatal heart attack. He explains that her father's property is now his. She excuses herself to go to her room. Instead she flees from the house, Jackson's men unsuccessfully trying to stop her.
Maria take her injured father to the church where the priest, padre Pablo, receive them. In the church there are a number of locals who have been evicted by Jackson's men, having nowhere else to stay.
Sitting outside her house, Sara is watching as her father's coffin is carried from the house in a procession.
Sara and Maria meet when they try to rob the town's only bank at the same time. Sara wants to take back her father's money in order for her to return to Europe, Maria is robbing it for the people who have been evicted and have nothing to live off. Jackson and his men arrive at the same time to inspect the bank's vault. The only thing left in the vault is a flower, left as a greeting by Sara. They stop at the church and get in a fight over how the money should be used, to help the people or for Sara to leave Mexico. They are interrupted by padre Pablo who take them to a cave outside the town where a large number of people is living, now that they have been evicted. Sara have a change of heart and they decide to rob banks together to help the people.
Outside the city live Bill Buck, a famous Texan bank robber, and he trains Maria and Sara to use weapons. Maria turn out to be a crack shot while Sara is quite good at throwing knives. When Maria falls into a river, Sara rescue her from drowning. "I guess this makes us friends" asks Maria. "I don't know about friends. But definitely partners" answers Sara. Before departing Buck teach them the three rules of robbing banks: One, nobody gets killed, two, don't take more than you can carry in one hand, and three, getting away is the first rule. The two start robbing friends, now known as the Las Bandidas on the wanted posters.
Arriving in the town of Santa Rita by train, the criminal investigator Quentin Cook comes to investigate the claimed fatal heart attack of don Diego. Sara and Maria meet padre Pablo in the church where he tell them that a detective has arrived from New York. They are interrupted by Cook himself knocking on the door of the church. Cook shows a photo of Sara as a child, asking if she and don Diego had any problems. The duo decide to go to Santa Rita to speak with Quentin.
In his room at the hotel, Quentin is getting dressed, wearing only a towel when Sara and Maria enter, dressed in dancer's costumes showing a lot of cleavage. They tie him up and have a photographer take photos of all three of them in provocative positions on his bed, threatening to have the set of photos sent to his fiance. When asking about his criminal investigation he tell them that he believe that don Diego was poisoned. Also, Sara teach Maria how to kiss a man, practising on Quentin.
They bring Quentin with them to the bank in town, showing the land deeds locked in the vault, explaining to him that Jackson is taking over land where a railroad will be built. In the office, Quentin find bottles of wine and a small bottle of poison. When Jackson's men unexpectedly show up at the bank, Sara and Maria manage to get away by taking a very compliant Quentin hostage. It is revealed that Quentin is the son in law of the president of the Capitol Bank. When he hears this, Jackson decide that capturing the Bandidas is the first priority, bringing in extra men.
Sitting around a camp fire in a forest, Quentin tell Maria of how a criminal can be found by looking for fingerprints at a crime scene. When Sara returns she complains of how difficult life has become now that she, a young lady, must live as a renegade without parents. Quentin explains that he would like to help them.
Maria and Quentin visit a bank, properly dressed as a young married couple, expressing an interest in depositing jewels for safe keeping. The bank is heavily guarded by Jackson's men. The bank manager is happy to show them the safe. Maria draw a gun and Quentin open the safe using his expertise. They blow a hole through the roof and leave the bank with a lot of money. Jackson's men are alerted by the explosion but find the bank robbed and their horses disappeared.
The governor and his ministers meet Jackson to express their deep concern that banks belonging to Capitol bank are not safe. Jackson show the governor how all the banks will be equipped with a new alarm system. Until all banks have been equipped, all money will be kept in the headquarters of the Banco de Mejico. Quentin and Sara visit that branch of the bank and hear of the new alarm system. With the help of an accomplice they get drawings of the alarm system and the keys to the vault.
Using a rope, a pair of skates and a blowgun with poisoned darts, the trio try to rob the Banco de Mejico of all its money. Instead they are captured by Jackson's men. Luckily they are freed by the locals, including Maria's father and padre Pedro.
At a meeting with the governor and his minister, Jackson promises that the gold reserve will be sent to Texas. The trio hears of this and decide to get their hands on the gold. In a quiet moment, Maria and Sara agree that they are now friends, not only partners.
The gold reserve is being transported to Texas by train. The Mexican governor, the president of the Capitol Bank and Trust and his daughter Clarissa are on the train. Jackson is also on the train, intending to use the train as a bait to capture the Bandidas. Before kicking the governor off the train, Jackson explain to him that he is going to keep the gold for himself.
The Bandidas enter the train with Quentin, have their revenge on Jackson and Quentin is reunited with his fiance Clarissa. In the end the Bandidas ride off together, heading for Europe where the banks are bigger.