Marty has an eccentric friend whom he calls Doc, Doc is an inventor. We see some of Doc's inventions and they seem to work well enough most of the time. Doc invites Marty to meet him in the parking lot at the nearby shopping center early one morning.
Here Marty is shown Doc's latest invention, a time travelling DeLorean, the car is of course nuclear powered. Keeping in mind that you can't just go down to the local hardware shop and buy some Plutonium. Doc acquired it from some terrorists whom manage to find him at this moment. They aren't happy that they don't have a bomb made from the Plutonium, and come in guns blazing.
Marty escapes in the car, but activates the time travelling mechanism, and is transported back 30 years to the mid 50's. He now has a few problems, one the Plutonium is all used up, and he inadvertently alters history, taking his father's place in the initial key encounter between his mother and father.
Marty manages to track down a younger Doc for help with the car, he also has to get his parents to fall in love with each other. All while not causing any major changes in history which could have disastrous consequences in the future.
Doc comes up with a plan to use the power from a lighting strike, Marty has the advantage of knowing when and where lighting will strike. The other problem isn't so easy, and the clock is ticking because he has to be in the right place at the right time to harness the lighting strike.
In the end it all works out, it is Hollywood after all. This can be watched with some of the kids, maybe not the younger ones, it is rated PG after all.