The late-18th- and early-19th-century U.S. soldier James Wilkinson enjoyed “one of the most extraordinary careers as a secret agent in the history of espionage,” writes Andro Linklater. Code-named Agent 13, Wilkinson provided Spanish authorities in North America with important information about American intentions and capabilities, even while he served as commander in chief of the U.S. Army. As Linklater also points out in this fascinating biography, Wilkinson’s actions were not exactly secret. Many people in the young republic—including its first four presidents—had reason to suspect his loyalties.

Born in Maryland in 1757, Wilkinson studied medicine in Philadelphia until the revolution intervened. He served ably under generals Benedict Arnold, George Washington, and Horatio Gates. During the pivotal Battle of Saratoga, he performed excellently as Gates’s chief of staff. Though clearly charming, ambitious, and talented, Wilkinson was always willing to let self-interest trump personal loyalty, and indiscretions he made involving Gates’s role in the “Conway cabal” against George Washington led to a duel with his former commander and ended Wilkinson’s role in the war.

He married into a wealthy Philadelphia family, but soon moved west to the Kentucky frontier. In 1783, he began a secret communication with Esteban Miró, Louisiana’s Spanish governor. Spain controlled the Mississippi; Kentucky needed the river to bring goods to Spanish-controlled New Orleans. The Mississippi was so important to Kentucky that Wilkinson assured Miró that he could use access to it as leverage to break the territory from the rest of Virginia and join it to Spain. Wilkinson suggested that Spain grant him a military commission. Instead, Spain agreed to pay him an annual pension for his services.

Wilkinson needed the money, especially after business losses prompted his return to the Army. He began spying in earnest. He also became embroiled in an ugly, backstabbing feud with his superior, Major General “Mad” Anthony Wayne. Wayne suspected Wilkinson of conspiring with the British, even as Spanish payments were making their way slowly up the Mississippi. The courier carrying the first payment of $6333, hidden in barrels of flour, was killed and robbed. In an episode spiced with enough chicanery to fuel an espionage thriller, Wilkinson and his cohorts managed to hustle the killers out of the region before they could expose Wilkinson’s double dealings—but it was a close thing.

Wayne’s death in 1796 vaulted Wilkinson to the Army’s top post, but stories circulated about his Spanish connections. The audacious Wilkinson even sent a letter to President John Adams welcoming an inquiry. Adams reassured him that he would “give no countenance” to “villainous rumours.” Thomas Jefferson, too, heard accusations against the general, but the president needed Wilkinson to placate an army angered by Jeffersonian policies. (Jefferson might have acted differently had he known that Wilkinson had informed the Spanish of the impending Lewis and Clark expedition and advised them to take its men prisoner.)

Wilkinson’s double life reached a crisis in 1806, when former vice president Aaron Burr schemed to separate the western