Just thought I'd warn you this is very inaccurate to what the book says but not completely.
A new year was about to begin at Hogwarts, which meant that all the first years needed their school supplies along with everyone else. Out of the many first years stood James Potter. Now James had always been one for trouble, and going to a school filled with people seemed like a great time for him to show it off.
Diagon Alley was busy like normal. Students running in and out of all different stores buying supplies and fun little gadgets to play pranks on their fellow students. Another first year with an abnormally large nose decided to head into one of the many bookstores. But his plan was foiled when he could not get past the door. Instead of simply opening the door himself he just continued to walk into it causing everyone in the bookstore to turn his or her head and look. Remus Lupin yet another first year decided to part himself from the book he was reading to help the poor student who couldn't open the door. He opened the door and the boy walked right over to the bookshelf.
"You're welcome," Lupin said hoping that he would be thanked. But instead the large nose child just kept looking at the books. Little did he know that James had set a trap for whoever pulled out a book from the shelf. The big nosed child reached out his hand and pulled out a book when a pile of green slime poured onto his head. Everyone in the bookstore laughed including Lupin who used his book to cover up his smile.
James stepped out of the shadows and bowed, all the kids clapped for him. The big nosed child wasn't happy and he walked out of the bookstore angrily. James rather proud of himself held up his head in joy. Suddenly a young first year by the name of Sirius Black walked into the store. He had long black hair, which was about as messy as James's was.
"Hello Sirius," the cashier at the bookstore said to him who just happened to be Andromeda Sirius's favorite cousin. He went up to her and asked for the books he needed. Not long after he entered two more of the black family entered the store. A girl with crazy black hair named Bellatrix, and a blonde haired girl name Narcisa.
"See those two over there Cissy?" Bellatrix asked as she pointed at Sirius and Andromeda, "You are never to talk to them unless you're threatening them. Got it?"
"Got it Bella," Cissy said in an evil preppy sort of way; unfortunately that is the way she talked all the time. Sirius even though he was one of the Blacks did not wish to have anything to do with his family. He was a lot like James when it came to causing trouble, and he currently was looking for a good person to play a prank on. He was considering Bellatrix or Cissy until fear of being punished by his parents or really any of his relatives forced him to choose a different target.
James who remained at the bookstore reset his prank in such a subtle way that no one noticed. Sirius was about to go grab another one of his books when Cissy pushed him out of the way.
"Move it looser," she told him. Usually this wouldn't intimidate Sirius but since Bella, who was a year older than him, was near he decided it was wise not to threaten her back. Cissy reached up to grab the book to find green slime pouring down on her bleach blonde hair.
"BELLA!" Cissy cried out, "Sirius dumped green slime on my head!" as she said that she started crying. Bellatrix approached Sirius holding her wand tight in her hand. But before she could say a spell she felt water splash in her face. As she fell backwards she saw Lupin holding his wand.
Sirius ran off, James and Lupin followed close behind him.
"Thanks mate," Sirius told Lupin.
"My pleasure," he replied, "I'm Remus Lupin by the way."
"Sirius Black."
"James Potter."
"Nice trick James how did you do that I can only get my pranks to work once," Sirius asked.
"It's easy all you have to do is," as James started to talk Lupin noticed Cissy and Bellatrix running towards them.
"Guys we should go," Lupin said told them. They all looked back and saw Cissy and Bellatrix so like what most normal people would do in this situation they ran. A fat little boy another fellow first year saw them running.
"PETER TO THE RESCUE!" he called out. He then jumped in front of Cissy and Bellatrix.
"What do you think you're doing?" Bellatrix asked him with her arms crossed in anger.
"This," as Peter said this he turned around and farted so badly that Bellatrix and Cissy both passed out.
"Thanks?" Lupin, James, and Sirius all said a bit puzzled by the strange boy's methods of self-defense.
"I know I know, but I'm sorry but no autographs today, but if yah don't know me my name is Peter Pettigrew," he told them, but they were still confused. They saw it getting late so they made their way off to the train. Peter, being who he was, decided to follow them. They all knew that great friendship was just beginning.