Marty is able to avoid serious injury. While riding on the hood of Biff's car, he distracts them by suddenly jumping up, jumping over the windshield and the backseat, and then hopping off. Biff and his friends are confused, and then see they are barreling towards a manure truck parked on the curb. They can only shout "SHIIIIT!!!!!" as the car slams into the back of the truck, which dumps its entire load of manure on them. Watching the chase from the diner, Lorraine becomes even more attracted to the adventurous Marty.
Back at Doc's shop, the inventor shows Marty how he'll use the lighting bolt to power the DeLorean. He'll string heavy cable down to the street, building a circuit. A hook attached to the back of the car will channel the energy from the bolt directly into the flux capacitor. The timing will have to be precise. The demonstration goes well, though it sets a garbage pail on fire. As Doc uses a fire extinguisher to put out the flames, they are interrupted by a knock at the door.
To Doc's shock, it's Lorraine, who has followed Marty. Doc and Marty quickly cover the DeLorean with a tarp before letting Lorraine in. Lorraine asks Marty if he wants to be her date to the Enchantment Under The Sea Dance. Marty attempts to back out, suggesting she go with George, but Lorraine balks at the idea, saying a real man stands up for the woman he loves, referring to the fight Marty just had with Biff.
Marty suddenly sees a way to get George to win Lorraine's heart. Marty approaches George while George is doing his parents' laundry, and tells him to find him with Lorraine in Doc's car in the school parking lot at a certain time, where Marty plans to "take advantage" of her. George is to pull Marty out of the car and pretend to beat him up, proving that he's the bigger man.
The night of the dance arrives. George is already there, in a tux, waiting for his cue, as the all-black band known as the Starlighters performs on the stage. At Lou's Diner, Marty writes Doc a letter on a piece of stationary warning. He slips the note into the pocket of Doc's coat while Doc is in the middle of using a $50 to bribe a cop who asks him if he has a permit for his "weather experiment". Marty arrives at the dance in Doc's car with Lorraine. As they stop, he asks her if they can "park" for a while.
Lorraine produces a small bottle of whiskey and begins to smoke, two bad habits she has in 1985. Marty warns her she may regret it later and Lorraine dismisses it, exasperated that Marty sounds like her mother. She also is aggressive in coming on to Marty in the car, much more than Marty had anticipated, though when she kisses Marty rather hard on the lips, she admits afterwards that she feels like she's kissing her brother.
Just then, the door is opened and Marty is pulled roughly from the driver's seat. But to Marty's shock, it's Biff, drunk, and seeking revenge for the $300 in damages Marty inflicted on his car in the manure truck accident. When Biff sees Lorraine in the car, however, he throws Marty to Match, Skinhead and 3D, climbs into the car, and begins to molest her. Match, Skinhead and 3D take Marty out behind the school and toss him into the open trunk of the first car they see, then slam the lid shut.
Unfortunately for them, the car belongs to Marvin Berry and the Starlighters. They scare Biff's gang off and they realize that the keys are in the trunk with Marty. George arrives at Doc's car, opens the door as planned, and delivers the lines Marty told him, but is taken off-guard realizing that he is not only dealing with Biff, but his "rescue" is now the real deal. He takes a half-hearted punch at Biff, who grabs his arm and begins to twist it. When Biff roughly pushes a pleading Lorraine off and begins laughing. George summons up the strength and courage, curls his left hand into a fist.
He punches Biff squarely in the jaw, knocking him out. Marty, freed from the trunk thanks to Marvin Berry himself, races to the scene just in time to see Biff knocked out. George takes Lorraine's hand and the two go into the dance hall. Marty, knowing that his future isn't sealed until George kisses Lorraine, goes back to the band and finds that Marvin is unable to play having injured his hand while freeing Marty from the trunk. Marty agrees to play guitar in Marvin's place and the band strikes up again, playing a romantic song ("Earth Angel").
Marty, already weak because his parents' love is not confirmed, begins to fade into non-existence when a fellow student cuts in between George and Lorraine on the dance floor. However, George regains his courage, takes Lorraine back and kisses her passionately. Marty is instantly revived and finishes the song and sees his mother and father happily in each others arms. Berry asks Marty to play another number with the band. Reluctant at first, Marty can't resist the opportunity and launches the band into "Johnny B. Goode".
While Marty plays, Marvin Berry calls his cousin Chuck (the soon-to-be-famous rock n' roll star), telling him that he found the "new sound" Chuck was looking for. Marty does Chuck Berry's trademark duck walk, and then gets carried away imitating other guitar heroes. Windmilling his arm and kicking over his amplifier in imitation of Pete Townshend, lying on the stage kicking his legs in imitation of Angus Young, playing behind his head like Jimi Hendrix, and tapping in the style of Eddie Van Halen.