On September 23, 1780, three Continental militia men stopped a  man riding  a horse south near Tarrytown, New York. He gave his name as John Anderson, and he seemed nervous and confused, so the men searched him. Hidden in his shoes, they found information about the Continental Army’s planned maneuvers and a detailed description of the construction and defenses of its fort at West Point.

The captive was Major John André of the British army, and he was in big trouble. Under normal circumstances, he would have been treated as a prisoner, but, since he was wearing civilian clothes, he was considered a spy and thus subject to execution. After being handed over to a colonel in the Continental Army, he wrote a desperate letter to General George Washington, explaining his actions and begging for mercy. It was to no avail; André was hanged on October 2.

The information André had been carrying came from the Continental general Benedict Arnold—the commander of West Point, a hero of several victories in New York and New England, and a fierce fighting general who Washington greatly valued. For a year and a half, he had secretly been feeding information to the British. The colonel who received André from the guerrillas, not realizing this, notified Arnold of André’s capture. Arnold fled immediately to a British vessel on the Hudson.

When Washington read the papers—at Arnold’s headquarters, where he had come to pay a visit—he ordered a pursuit of Arnold (which turned out to be fruitless), warned the garrison at West Point to be alert for a possible attack, and reshuffled the command at posts along the Hudson in case Arnold had placed collaborators in charge at those places. He also did his best to comfort Arnold’s distraught wife, Peggy. She pretended to be as surprised as Washington and his aides were by her husband’s betrayal, but in fact—as documents uncovered in the 1930s revealed—she had been deeply involved in the spy scheme, perhaps even its instigator.

After his defection, the British army put Arnold in charge of Loyalist troops. Following the British defeat at Yorktown in 1781, he and his wife moved to England, where they tried a number of businesses with little success, repeatedly begged a reluctant government for money, and found themselves widely ignored or even reviled. Before Arnold’s death in 1801 (Peggy died three years later), they could sometimes be seen visiting a monument in Westminster Abbey that memorialized “MAJOR JOHN ANDRE who … fell a Sacrifice to his Zeal for his KING and COUNTRY.” The monument still stands.