Hill Valley, California 1986

Marty opens the door to his house. Linda and Dave are busy working, and Lorraine is watching TV. Lorraine shuts the TV off, and walks up to Marty.

"Marty," She said, "There's a letter on the counter for you."

Marty looks at the counter and sees an old-looking letter. He picks it up. It says;

Dear Marty,

This is your old friend, Doc Brown writing. It's 1887 now. I sent this letter to the post office with specific directions to send it on this day and year. How are you? Hope well. We're ok, but a terrible thing has happened.
It all started on July 18, 1887. Clara was out with a friend, and I was at home, reading the paper. Jules and Verne were supposed to be doing their schoolwork. I had just folded the paper up to get a snack when I heard a loud crash. It sounded like it was coming from the garage. I went there, and saw that the DeLorean was gone! A huge hole was in the boards of the garage. I called for Jules and Verne. But they were gone.
Marty, you've got to understand. My sons are gone somewhere in time. And I have no clue when. I would tell Clara, but it seems that the town where her friend lives is in flooding. I couldn't tell Clara that our children were out somewhere in time. So, I told her that everything was fine. Which it's not. I will find some way to find the time that they are in.
So, I'm asking for your help. I have calculated the dates and time, so I know the exact date and year. I will come to 1986 for your aid. If we succeed or not, we'll return you to the exact minute you left.