September 21, 1780 at West Point at night: Maybe Asa was on guard duty? Major Andre came ashore from the British sloop "Vulture" which had sneaked up the Hudson and anchored just south of the fort. He met with the traitor Arnold (I don't know just how or where) who gave him documents including fortification plans.
During the night the Vulture was discovered and bombarded by American artillery so it withdrew down the river stranding Andre behind the American lines in his British uniform with the papers Arnold had given him. He took refuge in the house of one Joshua Smith, a Loyalist collaborator he had known in New York. When they discovered that the Vulture was gone they realized they would have to try to escape overland. Andre decided to don an American uniform for the trip. Bad mistake. If he had kept on his British uniform he would have been treated as a prisoner-of-war, but out of uniform he was treated as a spy when he was caught.
The next day when they thought they were safe in British territory Smith went home and Andre continued by himself, but he was stopped by a trio of American freelancers who searched him and found Arnold's papers. They promptly arrested him. Unaware of Arnold's involvement, a message was sent to him at West Point telling him what happened. He promptly took off and escaped downriver to the Vulture. On this same day George Washington unexpectedly arrived at West Point (Asa must have seen him and maybe saluted him?). There Washington learned of the arrest of the spy. When he was shown the confiscated papers he recognized Arnold's handwriting and realized he had been betrayed by his own General.
Andre was imprisoned at Tappan, New York, and on September 29 was tried by a panel of American Generals, found guilty of espionage, and sentenced to death. He asked to be executed by a firing squad like a soldier but at noon of October 2 he was hanged as a spy.
On October 21, 1780, Private Asa Pratt is dicharged and heads back to New Hampshire. One year later the Battle of Yorktown brings the Revolutionary War to an end.