The following is an excerpt from The Estrada Plot: How the FBI Captured a Secret Army and Stopped the Invasion of Mexico by Bill Mills (Potomac Books, April).

After months of living with only the barest of necessities while battling Obregón’s forces in western Mexico, Estrada was awed by his new surroundings in California. Everywhere he looked in the sprawling City of Angels there were signs of growth and prosperity.

Driven by the expanding oil, rubber, and film industries, Los Angeles was in the midst of an economic boom that would see its population soar from 577,000 residents in 1920 to more than 1 million by 1924, making it the fifth-largest city in the United States. More oil was being produced within the city limits of Los Angeles than anywhere else on earth, with towering derricks pumping rich crude out of oilfields stretching from the city center to the coastal beaches. Hollywood was now firmly established as the country’s film capital, and studios such as Warner Brothers, Famous Players–Lasky, RKO, MGM, and Fox were producing more than 80 percent of the world’s motion pictures on their vast production lots. Manufacturing was increasing at a fantastic rate, and the city’s six thousand companies shipped more than a billion dollars’ worth of products in 1924.

Estrada could feel at home in eastern Los Angeles, known as “México de afuera” (Mexico away) to the thousands of Mexican immigrants who had settled there, but other areas of the city seemed like another planet. Along LA’s teeming streets lined with palm trees a building boom was under way that would witness the construction of some of the city’s most iconic landmarks. The luxurious three-towered Biltmore Hotel, containing more than a thousand rooms and built in a magnificent blend of artistic styles, attracted a crowd of three thousand spectators at its grand opening in 1923. Not far away, work had begun on the twenty-seven-story Los Angeles City Hall, soon to become the tallest building in the city and one of its most distinctive landmarks. The skyscraper-like Central Library, adorned with limestone sculptures and topped with a pyramid at its summit, went up at the same time. The distinctive band shell and amphitheater seating of the Hollywood Bowl opened in 1926, with refinements continuing for decades.

The new architectural wonders—the “Los Angeles of tomorrow”—stood in sharp contrast to the buildings raised a generation earlier, now struggling to keep up with the city’s expanding population. Chief among these was the Post Office and Federal Building, an unpretentious six-story, triangular-shaped edifice in downtown LA that was completed in 1910 at a cost of $1.5 million. Even while construction of the federal building was underway, debate had begun about the need for a larger replacement. By 1924 working space for the federal agencies crowded inside the “Million Dollar Post Office” was at a premium.

On the top floor of the federal building four large offices were occupied by employees of the U.S. Justice Department’s Bureau of Investigation, which would later be renamed the Federal Bureau of Investigation. Situated among the mahogany desks occupied by the Bureau’s special agents, accountants, and stenographers was one aging employee whose unusual looks were not easily forgotten. Although the man was of average height and dressed in a conservative dark suit with vest and gold watch chain, his head was clean shaven and as white as the dome of the Capitol in Washington. He sported the long white mustache of a Cossack from the steppes of Eurasia and incongruously wore round, black-framed spectacles in the style popularized by the silent film star Harold Lloyd. To a casual observer his appearance might suggest that he was a Russian intellectual or philosopher—perhaps a Marxist?

But nothing could have been further from the truth.

He was in fact one of the most extraordinary special agents in the history of the Bureau of Investigation: Col. Emilio Kosterlitzky, known throughout Mexico as the “mailed fist” of the dictator Porfirio Díaz.

Born in Moscow in 1853, Kosterlitzky had entered the navy of Tsar Alexander II as a teenaged cadet in 1871. While serving as a midshipman on a training ship, he deserted to escape the grim conditions in the Russian navy. He made his move when the ship called at the port of New York. He then found his way to Guaymas, Mexico, where he joined the Mexican cavalry. In the decades that followed, the young Russian émigré took part in the seemingly endless campaigns waged by Mexico to pacify the Yaqui, Mayo, and Apache Indians, while rising steadily through the ranks.

Promoted to captain in 1885, Kosterlitzky transferred to the Gendarmería Fiscal, also known as the Rurales, a mounted force created by President Díaz to patrol the northern frontiers of Mexico and ensure that no trouble along the border imperiled the flow of American investment capital into Mexico. It was the job of the Rurales to keep the peace, but as one historian later noted, the Rurales were formed “not to catch criminals, or reform them, but to annihilate them.”4 Although the officers of the irregular force came from the army, the rank-and-file were drawn from jail cells and labor camps. Riding the lawless territory along the international line, the Rurales who came upon bandits or other lawbreakers pursued a result that was swift and certain. Díaz himself provided the maxim under which the Rurales operated: “catch them in the act, shoot them on the spot.” Suspects captured by the Rurales would be asked a few questions and, if the answers were not satisfactory, pronounced guilty and immediately executed. A trail of unmarked graves and bodies left hanging outside border towns and villages served as a warning to anyone foolish enough to contemplate making trouble in the areas patrolled by the Gendarmería Fiscal.

If not “law and order,” the Rurales at least maintained order.