Neither Chinese American leaders nor white officials in San Francisco made any real efforts to close the houses of prostitution that flourished in Chinatown in the 19th and early 20th centuries. Only one group of people stood up for the sex slaves imported from China to work in the brothels: Protestant missionaries, most of them women.

The past two Portals described how the prostitutes who tried to escape were severely beaten or killed by tongs, the secretive, brutal organizations that ran the brothels. Almost as horrific was the plight of another group of Chinese immigrants — little girls known as mui tsai who had been sold into bondage and worked as domestic slaves.

Of all the Protestant missionaries who fought for the victims, one towered above the rest: an indomitable woman named Donaldina Cameron.

As Mildred Crowl Martin writes in “Chinatown’s Angry Angel: The Story of Donaldina Cameron,” Cameron was born in 1869 on a New Zealand sheep ranch and came to California when she was 2. When she was a young woman, Cameron heard about a Presbyterian mission in Chinatown that rescued Chinese slave girls, called Occidental Mission Home for Girls, and decided to volunteer there for a year. She ended up giving her life to the cause.

When Cameron walked into Mission Home at 920 Sacramento St. in April 1895, she was greeted by its leader, Margaret Culbertson. That very day, Culbertson told her, tong members had placed sticks of dynamite on the house’s front porch. Did Cameron want to reconsider her decision?

A photograph of Cameron at the time shows an attractive 25-year-old woman with a hopeful expression, piercing eyes and a granitic set to the mouth. Cameron said no, she would not like to reconsider.

Cameron met the girls who were staying in the house. A 12-year-old named Chun Loie was typical.

Three years earlier, Culbertson was told that a 9-year-old mui tsai was being savagely beaten at the corner of Washington Street and Dupont Street, now Grant Avenue. Accompanied by police, Culbertson brought the little girl to the home.

“She was in pitiable condition,” Culbertson wrote in a ledger. Two cuts from a hatchet were visible on her head, and “her mouth, face and hands (were) badly swollen from punishment she had received from her cruel mistress.” The woman was arrested and fined $25 for cruelty to children.

Not all the stories had happy endings. In a ledger entry dated Aug. 15, 1892, Culbertson described the rescue of a prostitute named Sing Ho.

“She is very small of stature — looks like a midget — has an old and peculiar face — give her age as 22 years,” Culbertson wrote. “Sing Ho says her mother died in San Francisco and her father returned to China — that her parents owed money and that she entered upon a life of sin to pay their debts. Sing Ho was a victim of the opium habit and after spending a night in the Home decided to return to the brothel — she could neither eat nor sleep.”

A few weeks after she arrived, Cameron embarked on her first rescue. With Culbertson, an interpreter and two police officers of the Chinatown Squad, a special force created to patrol the district, she went to a squalid house on Bartlett Alley, now Beckett Street.

The police used sledgehammers to break through a window and found a terrified girl in a room. They asked if she wanted to go to Mission Home. “I come! I come!” the girl said. The girl’s “owner” ran in, screaming, “You break my house!” and abused the cringing girl in Chinese, saying, “May all your ancestors curse you, and turn you into a turtle!”

Then the girl was led away to safety.

Exhausted and in poor health, Culbertson resigned in 1897 and died soon after. Cameron was named Mission Home superintendent in 1900.

The rescue work was grueling, and the tongs constantly threatened her. At one apartment she was called to, she found an effigy of herself with a dagger through the heart.

She once shared a slave girl’s jail cell in order to free her. While she had the assistance of the Chinatown Squad, some officers accepted bribes to warn tong owners of impending raids.

Slave owners had spies throughout Chinatown, and would hide the girls in secret rooms or move them across rooftops or into cellars and tunnels. Cameron would chase them, sometimes catching up, sometimes not. The tongs also fought her in the courts, using unscrupulous white lawyers to draw up writs of habeas corpus, accusing their slaves of having committed crimes and obtaining search warrants to seize the girls.

Mission Home provided not just a safe haven for the 50 to 70 girls who lived there at a given time, but schooling, including Bible study, and training in sewing, cooking and other skills. Older girls took care of younger ones. The girls also went on outings to Golden Gate Park and to the beach.

Cameron was sustained by the love of her charges. One day, when she was riding on a ferry to Oakland with eight girls, a tourist woman heard one of the girls say, “It’s my turn to sit next to Mama.” The girls gave Cameron the Chinese name Lo Mo, which means “old mother.”

Cameron’s campaign to stamp out slavery in Chinatown went on for decades, with a tough but kind Chinatown Squad cop named Jack Manion providing indispensable help. The war was not won until 1935, when Cameron and her allies won a court case that smashed a major human trafficking network, sent some of its ringleaders to jail and deported others.

Cameron retired from Mission Home the year before. During her 39 years of service, she had rescued 2,000 to 3,000 girls from slavery.

Donaldina Cameron died in 1968. Today, the brick building at 920 Sacramento, which was renamed Cameron House in 1942, still serves the city’s Asian American community, offering a range of social services and popular youth programs.

And at the corner of Joice Alley and Sacramento Street, if you look up, you can still see the second-story corner room where one of San Francisco’s greatest heroes lived.

Gary Kamiya is the author of the best-selling book “Cool Gray City of Love: 49 Views of San Francisco,” awarded the Northern California Book Award in creative nonfiction. All the material in Portals of the Past is original for The San Francisco Chronicle. Email: metro@sfchronicle.com

Trivia time

The most recent trivia question: What is Hangtown Fry and how did it get its name?

Answer: An omelette of eggs and oysters. It was supposedly invented in Gold Rush Placerville, either by a newly rich prospector who ordered the most expensive dish in the house, or by a condemned man hoping to postpone his execution while oysters were obtained.

This week’s trivia question: Where was Happy Valley?

Editor’s note

Every corner in San Francisco has an astonishing story to tell. Gary Kamiya’s Portals of the Past tells those lost stories, using a specific location to illuminate San Francisco’s extraordinary history — from the days when giant mammoths wandered through what is now North Beach to the Gold Rush delirium, the dot-com madness and beyond. His column appears every other Saturday, alternating with Peter Hartlaub’s OurSF.