Marty: The almanac! (Doc chuckles again) That son of a bitch stole my idea!
Marty slams his fist on the table.
Marty: He must have been listening when I..... it's my fault! If I hadn't bought that damn book, none of this would ever have happened!
Doc: Well, that's all in the past.
Marty: You mean the future.
Doc: Whatever! It demonstrates precisely how time travel can be misused and why the time machine must be destroyed - after we straighten all of this out.
Marty: Right, so we go back to the future, and we stop Biff from stealing the almanac.
Doc: We can't! Because, if we travel into the future from this point in time, it will be the future of this reality! (He underlines 1985-A on the board). In which Biff is corrupt, and powerful, and married to your mother; and in which this has happened to me!
Doc shows Marty another paper. The headline says "Emmett Brown Committed - Crackpot Inventor Declared Legally Insane." A side story says "Biffco To Build New Dioxin Plant" and "Nixon To Seek 5th Term." Einstein whines as Marty takes it.
Doc: No, our only chance to repair the present is in the past, at the point where the timeline skewed into this tangent. In order to put the universe back as we remember it, and get back to our reality, we have to find out the exact date, and the specific circumstances of how, where and when, young Biff got his hands on that sports almanac.
Marty: I'll ask him.
Cut to the movie "A Fistful Of Dollars". Clint Eastwood looks up to the camera. The other guy shoots him, and Clint falls into some barrels. The other guy smiles, and fires again - he's out of bullets. Clint gets up and reveals the bullet-proof vest. Cut to Biff. He's in his jacuzzi with two women, all 3 watching the movie.
Biff: Bullet-proof vest! Great flick, great frigging flick The guy is brilliant!
Marty comes up behind and turns the TV off using the remote.
Biff: Hey, what the hell's going... (sees Marty) Ah!
Jacuzzi Girls: Ahh!
Marty: Party's over Biff.
He throws the remote in the jacuzzi.
Marty: Sorry ladies.
Biff: How'd you get past my security downstairs?
Marty: There's a little matter we need to talk about.
Biff: Yeah, money, right? Well forget it!
Marty: No, not money. (slowly) Grays Sports Almanac.
Biff looks horrified - how did Marty find out?
Biff: You heard him girls, party's over.
Cut to Biff. He enters a room wearing a robe. Marty follows him. In the room is a big painting of Biff.
Biff: Start talking kid, what else do you know about that book?
Marty: First, you tell me how you got it. How, where, and when.
Biff: Alright, take a seat.
Marty stays standing. Biff walks over to the painting of himself. He turns to Marty.
Biff: Sit down! (He does) November 12th 1955, that was when.
During the following Biff reveals the painting is really a safe! He opens the safe.
Marty: November 12th 1955? That was the day I went back... (covering) that was the day of the famous Hill Valley lightning storm.
Biff: You know your history, very good. I'll never forget that Saturday. I'd just picked my car up from the shop because I'd enrolled it in a drag race a few days earlier.
Marty: I thought you crashed it into a manure truck.
Biff: How do you know about that?
Marty: (covering) My father told me about it.
Biff: Your father?
Marty: Before he died.
Biff: Yeah right. So there I was, minding my own business (he opens the safe) when this crazy old codger with a cane shows up.
Biff takes a box out of the safe.
Biff: He says he's my distant relative. I didn't see any resemblance.
He puts the box on the table.
Biff: So he says "How would you like to be rich?" So I say "Sure."
Biff opens the box and takes the sports almanac from it.
Biff: So he lays this book on me. He says this book'll tell me the outcome of every sporting event 'til the end of the century. All I have to do is bet on the winner, and I'll never lose. So I say "What's the catch?" He says, "No catch, just keep it a secret."
Biff puts the book back in the box and closes it.
Biff: After that he disappeared. I never saw him again.
Marty takes a "Biff's Pleasure Paradise" matchbox and puts it in his pocket.