Marty meets up with Doc, your typical mad scientist type, his dog Einstein, and… a car. A DeLorean, specifically.
The camera starts rolling, and Marty records Doc explaining that he's built a time machine. He proves it by sending Einstein one minute into the future.
Doc shows Marty how it works, and introduces him to the "flux capacitor," which is what makes time travel possible. But here's the kicker. The thing runs on plutonium. How did Doc get a hold of such a thing, you ask? Eh, he ripped it off a group of Libyan nationalists. We can't see a down side.
Oh: here's that down side. The Libyans show up, pepper Doc with bullets, and nearly do the same to Marty… but he luckily escapes via the DeLorean. To 1955. Out of the frying pan and into the fire.