Two riders rode determinedly to Benedict Arnold’s headquarters at the Robinson House across the Hudson River from West Point on the morning of September 25, 1780. The lead courier, Lt. Allen, who had initially been accompanying the captured “John Anderson,” carried with him the letters written by Lt. Col. Jameson informing Arnold of Maj. John Andre’s capture and his subsequent retrieval and return to the American camp at South Salem; the second rider possessed the incriminating papers found on Andre relating to West Point, as well as a newly signed confession the British officer had penned the day before admitting who he was. The second set of documents was meant for George Washington, who was to arrive at Robinson House to meet with Arnold and inspect the fortifications that day. It was a race against time between the two horsemen, and Arnold’s rider had the lead.
Washington was due to arrive at Robinson House for breakfast with Benedict and Peggy Arnold, but he chose to take a quick detour and inspect several American redoubts before continuing on his path from Fishkill, New York, where he had spent the evening. Instead, two of his aides, James McHenry and Samuel Shaw, were sent ahead to inform the couple to begin breakfast without him. Upon their arrival, the men sat down with the general to eat, informing him that the commander in chief would be there shortly. During this, Peggy remained upstairs.
After a few moments, Arnold excused himself from the table and stepped away to issue some daily orders. It was at this time when the walls of Benedict Arnold’s world began to close in on him. Lieutenant Allen had arrived with the news of Andre’s capture and transfer to the American camp at South Salem. The letter from Jameson also informed Arnold that the dispatches Andre carried were forwarded to Washington. If his treasonous plot had not yet been discovered, it was only a matter of time before it was. McHenry and Shaw had shown no signs of suspicion, but did Washington already know?
As the reality of the situation overtook Arnold, he ordered his horse saddled and his boat’s crew to man the vessel below on the Hudson, and told one of his aides, David Franks, that he was travelling upriver to West Point and would be back shortly—he was preparing to make a hasty escape. Before leaving Robinson House, he quickly found Peggy and explained to her that his life was in danger and he needed to leave (if Peggy was truly part of the plot, then what was actually said will probably never be known and was left out of later recollections to avoid incriminating her as well), he then mounted and spurred his horse down toward the river. After entering his barge, he ordered the crew to take him downriver to Stony Point, where he had business to attend to. As the vessel began to sail, an armed American boat passed closely by, and the quick-thinking Arnold told its crew to go up to Robinson House and inform Washington when he arrived that he would be back before dinner. They continued south, and even outran the other craft when it turned around and began to follow them in the other direction.
When Arnold’s crew finally reached Stony Point, his request of them changed dramatically. Offering up two gallons of rum, he ordered his boatmen to carry him further downriver to the enemy vessel Vulture, which was originally supposed to carry Andre to the British lines. Instead, Arnold would be the one who boarded the boat and made his way to New York City, in the process taking the Americans who had just sailed him to safety as prisoners. Arnold’s defection was complete, but his plot to turn over West Point had been foiled.
An hour so after Arnold made his escape, Washington arrived at Robinson House. The commander in chief made his way across the river and was disgusted by the condition of the American defenses. The absence of Arnold perplexed him, but he did not think anything of it until he and his subordinates returned to the general’s headquarters and were greeted by the arrival of the second messenger carrying the Andre documents. Arnold’s treachery was thus revealed to the American high command, and immediately Washington ordered several aides to move downriver and see if the traitor’s vessel had been held up. It was too late, however. Arnold was gone, and as the reality of his betrayal began to set in for Washington (who had always been one of Arnold’s most ardent supporters) the general turned to the Marquis de Lafayette and asked him, “Whom can we trust now?”
Although Arnold had beat a hasty retreat to New York City, Peggy still remained behind at Robinson House. From the Vulture’s deck, her husband had scribbled off a message to Washington pleading with him for her safety and declaring her ignorance to the entire scheme. There are many versions of what transpired next, but according to the American officers at Robinson House, Peggy Arnold broke down in hysterics, seemingly going mad at the news of her husband’s treason. According to Col. Richard Varick, one of Arnold’s aides who was recovering from a fever in the house, a shriek was heard and the staff officer found Peggy with her hair “disheveled and flowing about her neck; [in] her morning gown with few other clothes remain[ing] on her—too few to be seen even by a gentleman of the family, much less by many strangers.” She then proceeded to ask if he had ordered her child to be killed and to “spare her innocent babe.”
It has been long debated if this was a genuine outburst of hysteria for Peggy, or if she was putting on a show to shield her own involvement in the plot. Multiple times Peggy was calmed down by the American officers arriving at the house, but her outbursts commenced again. Screaming about her husband, she was assured that he would return soon from West Point with Gen. Washington. Pointing to the ceiling she cried, “the spirits have carried [him] up there, they have put hot irons in his head!” Then the hot iron went from Arnold’s head to her own and only Washington could remove it. With this, the general was brought in to see and she accused him of being an imposter. Peggy’s frenzy continued into the early evening when finally she regained control of herself and but still felt the despair of what had happened that day. If this was all a ploy, she had forced Washington, Lafayette, Alexander Hamilton, Varick, and countless to fall hook, line, and sinker for it. She was safe.
That evening, Washington and those who accompanied him sat down for dinner and pondered the gravity of the situation. It is impossible to image the anger, betrayal, despair, and heaviness that they must have felt. The American Hannibal was now the American Judas.
“Arnold has betrayed us. Whom can we trust now?”
 Quoted in Stephen Brumwell, Turncoat: Benedict Arnold and the Crisis of American Liberty (Yale University Press: New Haven, CT, 2018), 278.