On Sunday morning on March 27, 2016, Miriam Rodriguez was hiding and holding a loaded .38 pistol near the Matamoros International Bridge, which links Matamoros, Mexico, and Brownsville, Texas.

Wearing a baseball cap and trench coat, the 56-year-old mother-of-three was waiting for a member of the feared Zeta drug cartel known only as “The Florist. “

Two years prior, he had been one of 11 men involved in the kidnapping of her then 20-year-old daughter Karen. Now, Miriam was out for justice — and revenge.

Spotting the Florist near some street vendors, Miriam pulled her gun and seized the moment. She grabbed his shirt and jammed the pistol into his back.

“’If you move, I’ll f–king shoot you,’ she said, going on to hold him at gunpoint and perform a citizen’s arrest until police arrived.

Author Azam Ahmed portrays this dramatic scene in the his new book “Fear Is Just A Word – A Missing Daughter, a Violent Cartel, and a Mother’s Quest for Vengeance” (Random House). It tells the story of how, for years, Miriam relentlessly pursued the men who had taken her daughter.

It’s also the tale of how drugs, violence and lawlessness can all but take over a country, leaving its citizens to take the law into their own hands, just as Miriam did.

“Criminals thrived on the permissiveness that fear allowed; she was a one-woman example of how things might be different,” writes Ahmed. “Miriam had said that fear was just a word. To the Zetas, it was much more than that.”

Miriam first learned of her daughter’s kidnapping when she was living and working as a housekeeper for a pair of doctors in McAllen, Texas, after she split up with husband, Luis, and moved north.

Her daughter, Karen, remained behind and ran the family’s cowboy store, Rodeo Boots, in San Fernando.

The former cattle-ranching town had become infamous in 2010 when the Zeta, having split from the Gulf Cartel crime syndicate, killed 72 migrants in the so-called “San Fernando Massacre.” In 2011, they kidnapped and butchered 192 people at La Joya ranch in the town.

On January 24, 2014, they struck the Rodriguez family. At 4 a.m. that morning, Miriam got a call from her eldest daughter, Azalea, telling her that Karen had been taken.

The kidnappers had called Karen’s father, demanding a ransom of 1 million pesos (around $77,000), payable by 3 p.m. the following day for her safe return.

On January 24, 2014, they struck the Rodriguez family. At 4 a.m. that morning, Miriam got a call from her eldest daughter, Azalea, telling her that Karen had been taken.

Then they put his daughter on the line, as Ahmed writes. “‘If you pay them, they will let me go’ Karen said. ‘If not, then I guess this is goodbye.’”

Soon after, the kidnappers called Miriam in Texas, outlining their demands again.

Miriam dropped everything, left a note for her employers, and returned immediately to San Fernando.

The next morning, meanwhile, Luis headed to the bank to empty their savings account and arrange a loan for the remainder of the ransom.

But when they dropped the money off, as arranged, there was no sign of Karen. “As the hours passed and darkness fell over San Fernando, an unspoken fear began to seize each of them,” writes Ahmed.

“What if Karen wasn’t coming back?”

The fact that Miriam and Luis had paid the ransom with such speed had led the kidnappers to reconsider.