His wife Margaret "Peggy" Shippen was a spy

One of the most interesting facts about Benedict Arnold and Peggy Shippen is that his wife Margaret "Peggy" Shippen was a spy. She was the second wife of General Benedict Arnold and the highest-paid spy in the American Revolution. On April 8, 1779, she married Arnold. Despite military regulations on communicating with the enemy, Shippen and her pals found ways to stay in touch with paramours across the combat lines. Some of this communication was made possible thanks to the efforts of Philadelphia merchant Joseph Stansbury.

Arnold met with Philadelphia merchant Joseph Stansbury in early May 1779, who then went surreptitiously to New York with a tender of Arnold's services to Sir Henry Clinton. Stansbury defied Arnold's orders not to engage anybody else in the operation and crossed the British border to see Jonathan Odell in New York. Odell was a Loyalist who worked with William Franklin, the son of Benjamin Franklin and the final colonial governor of New Jersey. On May 9, Franklin brought Stansbury to Major André, the newly appointed British intelligence head. This was the start of Arnold and André's secret correspondence, which included his wife Peggy as a willing intermediary at times, and culminated more than a year later with Arnold's switch of sides. Many historians believe she helped Arnold's efforts to switch sides by secretly negotiating with her friend André and relaying their signals to one other.