Thank you to @BChill12 for the idea!! This one is probably going to bounce between Biff's and the reader's POVs and might be a couple of parts, enjoy! 

Your POV 

"We have to go find Doc before we run into one of your parents!" I said as I looked at Marty. Looking at the slightly taller teenage boy, he sighed gently. Putting his hands on his hips he shuffled his weight for a second before running a hand in his hair. 

"I know, (y/n)." he said as he spun around in his pacing. Watching him for a second I rose a brow before I grabbed him. "McFly stop freaking out for like half a second." I said as he looked at me. Nodding gently as he took a breath I started talking. 

"All we have to do is figure out where Doc lives, didn't he say that he had a giant house once when he was monologuing?" I asked and he thought for a moment before nodding. "I think so, something about how he spent his whole family fortune trying to make the time machine work." he said. 

Smiling at him I let go of his orange vest. "Good, so all we have to do is figure out where the Brown residence is, Doc should be around his thirties or so during this year, right?" I said and he agreed. "Let's see if we can find something that'll give us an address." he said as we made our way into town. Walking with him I glanced at him as he was a bit ahead of me. We had been pretty close since we've met, nowadays we're more like siblings and he sees me as nothing more than a younger sister. 

Though I don't think that's a bad thing since he's taken a swing or two for me because some random deuce was giving me a hard time, so he's always been a brother figure. Crossing the street as we got to the downtown square in front of the courthouse we crossed the street into the same diner that we often went to for lunch on the weekends. 

Getting inside I looked around and smiled. Asking the chef that was standing behind the counter if he knew if there was any Brown's in Hill Valley. He smiled at me for a moment and nodded. "The only Brown that I know of is Emmett, but he's an old cuckoo, what do you want with him?" he asked as he wiped the counter down in front of me. 

Smiling gently I hummed. "We're old friends with him. We haven't seen him in some time, so we were thinking on stopping by, and we haven't been in town since we were really young." I said. Marty rubbed the back of his neck as he often did when he was nervous about something. The chef that I had figured was the owner  of the diner until his son got it in the 80s. 

"There's a phonebook in the back over by the payphone you can look in." he said and I smiled as I thanked him. Going over to the small booth with Marty i grabbed the book and flipped through the pages, looking for Emmett L. Brown, I hummed gently. Finding it I smiled gently before I put my finger on it and pointed. "There it is, 1640 Riverside Drive." I said and tapped on it. 

Looking at Marty as he dialed the number to see if Doc would answer, after listening to it ring, he put the phone back on the base and sighed gently. Closing the book after writing the address down on my arm, we left the diner and made our way across town. We were almost there until Marty saw someone fall out of a tree in the middle of the road, before he ran over and pushed him out of the way and got hit by the car himself. Sighing heavily as he got carried inside, I thought about who that was in front of the car. 

Groaning as i shook my head, not only did Marty keep his dad from getting hit by the car, he ended up changing how his entire conception was supposed to happen, since Lorraine is now gonna fall for Marty and not George. Damnit McFly, can't take you anywhere. Deciding that he would be fine on his own while Lorraine kept an I on him, I kept heading to Doc's. Hopefully he would have enough sense on what to do. 

~The Next Day~ 

Hearing a knock on the door as I got up from the couch I grumbled a little as I had gotten woken up. Walking over to see who it was, I was woken up immediately as I saw the familiar puffy orange vest. Opening the door and tackling him with a hug as he caught me I smiled. "You're alright, how's your head?" I asked as I grabbed his face and moved his head around as I looked at it. 

He grabbed my hands and nodded gently. "I'm fine" he said as he looked behind me to see Doc. "Seems you found Doc okay, did you tell him what's been going on?" he asked as he followed me inside and I nodded. "He's all caught up, did your mom get the hots for you?" I asked and smirked. He groaned and sighed. 

I looked at Doc to see that he had a confused look on his face. Humming gently I sighed. "He pushed his had out of the way of getting hit by his grandpa's car which was how his parents met when they were teenagers, making his mom fall for his dad, and then they go to the dance and then end up together." I said. He nodded gently and crossed his arms. 

"It's called the Florence nightingale affect. It happens when nurses fall for their patients." he said and I nodded. "How do we fix it?" Marty asked and I looked to Doc as he thought for a moment. "You two are going to have to go to school and trail his pop, and figure out how to get them together. Your Mom has to notice your dad before the dance that's supposed to happen next Saturday so we can get you two Back to the Future." 

~ 

There's part one, part two will be added soon. 

(1070 words)