Doc's letter was a three-page letter sent to Marty McFly from Emmett Brown — via several generations of Western Union — while he was trapped in 1885. After settling down as a blacksmith, on September 1, 1885, Doc gave the letter to Western Union with the explicit instructions that it be delivered on the highway in front of the future Lyon Estates to a person responding to the name of "Marty McFly" on November 12, 1955, the same place and time as when he disappeared when lightning struck the DeLorean time machine.