Doc's wife Clara had sent Marty a letter from 1893 via several generations of Western Union, letting him know that Doc had disappeared into the future. When Doc discovered the note in his secret lab in 2035, he was confused since he wasn't in trouble. However, shortly afterward he lost his memory by an electric jolt shot by Officer Griff Tannen. Amnesiac and confused, Doc reached into his pocket, found Marty's note, and went to the location and time specified in the note.