WASHINGTON: No power couple cut a wider social swath in post-Civil War Washington than President Ulysses S. Grant’s attorney general, George H. Williams, and his wife, Kate.

Then Kate Williams’ abandoned son from a previous marriage spoiled things by showing up in the capital, gambling — sometimes bringing them to receptions at the Williamses’ grand home on Rhode Island Avenue. He financed this embarrassing lifestyle by blackmailing the attorney general.

So George Williams called in the chief of the Secret Service, Hiram C. Whitley. Get rid of my stepson, he said, and do it quietly. No blood.

Whitley promptly obliged. Undercover Secret Service men got the youth drunk, convinced him, after he regained consciousness, that he had committed murder while intoxicated, then helped him “escape” to Veracruz, Mexico — where they abandoned him. He never bothered the Williamses again.

Now that’s a Secret Service scandal. At least it would have been, if the story had come out before Whitley told it decades later in his memoir, a book that few people read in the year of its publication, 1894, and even fewer have read since.

Still, the tale provides a dash of historical context for the travails of today’s Secret Service, an agency justly proud of its record but never free of controversy, even in its earliest days.

Congress established the Secret Service as a division of the Treasury Department in 1865; its mission was to combat counterfeiting of the new paper currency issued during the Civil War. As such, it was the first-ever federal detective force, long before the FBI. (The Secret Service still investigates counterfeiters; it did not take on presidential bodyguard duty full-time until after the 1901 assassination of William McKinley.)

Hiram C. Whitley was its second chief and a genuine innovator. During his tenure, which began in 1869, the Secret Service instituted a written code of conduct, developed files on criminals, photos included — and authorized the first Secret Service badges.

Whitley busted not only counterfeiters but also smugglers of cigars, liquor and diamonds in New York. Long before J. Edgar Hoover’s 10 Most Wanted, Whitley manipulated the press with juicy leaks and colorful tales of his agents’ exploits.

Whitley’s finest hour was the Secret Service infiltration of the Ku Klux Klan. At the special request of the Justice Department, his disguised operatives fanned out across the South, gathering intelligence — often with the aid of African Americans — that helped bring white terrorists to justice.

The crackdown enabled black voters to participate freely in the 1872 elections. Whitley boasted lavishly of this noble effort, yet he was hardly noble by nature. A teenage runaway whose pre-Civil War resume included fraudulent pawnbroking in Massachusetts and kidnapping fugitive slaves in Kansas, he had served during the war as a hit man for the Union army in New Orleans.

In short, for Whitley, law enforcement and covert operations were more of an adventure than a mission — and the ends always justified the means.