At the age of fifty, a California housewife named Mary Brenner Clarke left her comfortable suburban world and began to serve the poor inmates of La Mesa, one of Mexico's worst prisons. Living in one of the prison's cells, "Mother Antonia" serves everyone from rapists to drug dealers to petty thieves. Excerpted from "The Prison Angel" with permission of the Penguin Press.

The more inmates Mother Antonia met, the more she was struck by how many of them didn't deserve to be locked up. She often meets people who believe that everyone in prison probably deserves to be there, but in La Mesa she discovered that is anything but the truth. She found the prison was choked with inmates who had committed the slightest of crimes, many of whom had stolen food to eat. She met some serving long sentences for stealing a jacket or a pair of shoes. Many were simply awaiting trial and didn't have bail money, and hundreds more had been convicted of misdemeanors and ordered to pay as little as a twenty-five-dollar fine in lieu of jail. They didn't have the money, so they had to do the time. Others were lost in the system, stuck in prison beyond their release dates because of abysmal record-keeping or other administrative blunders. A Guatemalan house painter spent more than a year in La Mesa because police were sure he was a Mexican man wanted for robbery. A sympathetic human rights group finally proved that he was the wrong man-their photos looked nothing alike-and he went free after losing fifteen months of his life. The Mexican justice system, like many around the world, is stacked against the poor. The wealthy use high-priced lawyers and political connections to stay out of prison, while poor people who commit petty crimes are locked up. Bankers and politicians who have embezzled millions walk around free, but the system comes down like a sledgehammer on minor offenders. We have come across many such cases, including a man sentenced to three years for stealing a Gansito, a sweet roll like a Twinkle, and another who served six years for stealing bread. A college student who used a fake ID to get on the Mexico City subway, instead of paying the twenty-cent fare, served two months in prison and paid a fifteen-hundred-dollar fine. Poorly trained police tend to focus on the easiest crimes to solve, like street robberies, while legislators under political pressure to combat rising crime rates set tough minimum sentences for the smallest of offenses. The inequality reminds Mother Antonia of a quote from Bishop Oscar Romero, a personal hero of hers who was murdered in El Salvador in 1980: "The law is like a serpent. It bites the feet which have no shoes on." Mother Antonia quickly realized after moving into La Mesa that she could free many prisoners, mainly first offenders convicted of nonviolent crimes, by paying their bails or fines. She looks at a donated hundred-dollar bill and sees four free men. So she started visiting courthouses all over Tijuana and the rest of Baja California state, pleading for mercy and paying the fines of thousands of men and women. She also started representing prisoners at their court appearances. The first time was to plead the case of a young couple who had been convicted of helping smuggle people across the border into the United States. The couple, who were raising a baby in La Mesa, worked at the prison cleaning and ironing for wealthier prisoners to raise money to pay their fine. They were still about a thousand dollars short when Mother Antonia went to court to plead for their freedom, telling the judge that they had never broken the law before, they were never violent, and they had been exemplary prisoners. The judge waived the rest of their fine, and they were released. As she became a familiar sight in the courthouses and got to know the judges better, Mother Antonia began raising the issue of the unfairness she saw in sentencing. She repeatedly saw those who killed a wealthy person sentenced to twenty-five years or more, while those who killed a poor person got off with as little as four years. "Isn't everybody's life just as valuable?" she asked Miguel Angel Barud, a judge in Tijuana.

Barud, who calls Mother Antonia a "refreshing Coca-Cola in the desert," says her persistent arguments changed the way he sentences people and reminded him that a victim's social standing must be irrelevant. "There are fewer and fewer people who worry about others in this world," the judge says. "I wish there were more Mother Antonias."