In chapter 26 of The Spy, Captain Henry Wharton is charged with passing the pickets of the American army in disguise for the purposes of espionage. Wharton, an officer in the British army, makes a convincing case that his only purpose in disguising himself was to visit his elderly father. At this point, the result of the trial is still uncertain, but Major Dunwoodie's testimony in Wharton's favor makes a good impression, and Wharton has some hope that the statement of his sister, Frances, will assist him further.
The turning point comes when Frances innocently mentions that, during Wharton's visit, he spoke to their neighbor, Harvey Birch. Although Birch is, in fact, a spy for the American side, many people, including those presiding over the court, suspect him of being a British spy. For Wharton to have had dealings with him is regarded as such damning evidence as to be practically proof of guilt. The colonel who is interrogating Frances turns pale and shrinks "as from the sting of an adder" at the very sound of his name, while Major Dunwoodie cries out that Wharton is lost and runs from the room. The moment Harvey Birch's name is mentioned, therefore, Wharton's conviction for spying becomes a certainty. He is sentenced to be hanged the next day.