Back at Doc's swanky pad, they hook up the video camera to the TV (incredibly, the 1985 cords are still compatible with 1955 electronic equipment). Doc watches his older self in amazement and delight but goes a bit ballistic when he gets to the part about the 1.21 "jigowatts" of electricity. If it had been us, we think our threshold for shock would have been lowered after hearing someone say, "I'm from the future."
Since the procurement of plutonium is not really an option in 1955, they stumble upon the ingenious and oh-so-fortunate idea of using a bolt of lightning—the one that is due to screw up the clock tower in about a week—to generate the power needed to send Marty back to 1985.
So he's got a week to chill…but unfortunately, it's not going to be much of a relaxing vacation. Because he bumped into his parents and threw the course of history all out of whack, Doc informs Marty that he's got to figure out a way to get mom and pop back together, or there won't be a Marty McFly to send back to the future.