It's amazing how tiny little decisions can make all the difference. Even something as simple as choosing where to sit on a train can change the course of events for the next two years of your life.

And so it was that August went by at the slowest pace imaginable. But, as the calendar promised, September finally arrived and it was time for me to start school. Hogwarts! I barely slept the night before, and I was annoyingly talkative on the way to King's Cross. Ever vigilant, Mum put up with me and got her own back by making an overly-motherly fuss at the platform before finally, after far too many hugs and "have fun"s and "have you got everything?"s, letting me board the Hogwarts Express. That steam engine sure was like nothing I'd ever seen before. Yes, it was a muggle contraption, but there was just something extraordinarily magical about that train.

This was an important moment. Who knows where my life would have taken me had I not chosen the carriage I did? I like to think I would have ended up exactly where I am right now, just via a different path. But there's no way of knowing, so I'm glad I pulled open the door to the first carriage I saw, though it was several years before I was.

"Mind if I sit?" I asked the carriage as a whole, but it seemed only one of the three acknowledged the fact I'd just entered, even if it was only with a curt nod in my direction without even looking at me. I quickly hoisted by trunk up onto the luggage rack and sat down in the nearest available seat, next to the boy who'd nodded at me.

"Draco Malfoy," he said as way of introduction. "I'm going to be in Slytherin. It's the only house worth being in, my father says. Gryffindors are reckless imbeciles, Ravenclaws reckon they're all a bunch of geniuses and Hufflepuffs are completely useless! You don't come from a Hufflepuff family, do you?"

"No-"

"Good. They say people in the same family often end up in the same house. Take my family, for example. We've all been in Slytherin, for generations. I think we did have a Ravenclaw once, but he was married in, he doesn't really count. I can't imagine marrying someone from another house, could you? I'd hate to dirty the Malfoy name by giving it to some scum outside of the Slytherin house. Oh, and this is Crabbe and Goyle," he added. The two boys sitting opposite grunted in unison. "Who are you?"

Draco looked at me for the first time then. What are you expecting now – that his blue eyes shone like the ocean? That, in that moment, a connection sparked and I knew he was my soulmate? Well, I hate to burst any bubbles, but it doesn't always happen that way. In fat, I don't know any couple who met like that. When Ginny and Harry first met, she gave a small scream and ran out of the room. When Ron and Hermione first met, she told him he had dirt on his nose. Neville and Hannah barely glanced at each other for years. And I barely got a word in edgeways while Draco went on about how Slytherins are so much better than everyone else.

"Abbie Riddle," I replied. (Much quicker than the length of that paragraph implies.)

"Riddle? I don't think I've heard that name before. You're not a mudblood, are you?"

"No, I'm pure-blood." Or so I thought at the time. "All my family have been in Slytherin too." Let's not tell him that only included two people...

"Clearly not very good Slytherins," Draco sneered, "or I would have heard of your name. My father's Lucius Malfoy you see, perhaps you've heard of him? He's extremely powerful. Anyway, he's friends with a lot of great people, there's not a single witch or wizard with any status who doesn't know his name."

"Excuse me," came a bossy voice from the carriage door, which had just been opened. "Have any of you seen a toad? A boy named Neville's lost one."

"Yes, I have," Draco replied.

"Oh, excellent! Where?"

"I'm looking at it."

I have to admit – because it's a vital point – I laughed. Only shortly, but I laughed. It's vital because that laugh immediately connected me to that rude blonde boy in Hermione's mind, just one of the reasons why choosing that carriage to sit in would later look like a terrible idea.

Once Hermione had stormed off, Draco began laughing, and Crabbe and Goyle laughed (or grunted repeatedly, more accurately) with him.

"Did you see her face?" Draco said between fits of laughter. "It's her own fault for looking like a toad. Stupid girl can't even shut a door. Crabbe, shut it, will you?"

Crabbe grunted and stood up to do so. "Hey, Malfoy," he said, "someone outside just said Harry Potter's on the train."

This sparked Draco's attention and, granted, mine. "Where?" He stood up and practically fell out of the carriage door. (He disagrees, by the way. He thinks he walked out of the door quite calmly, but I know what I saw.) "You there. What's this I hear about Harry Potter being on the train?"

"I saw him get on!" The girl squealed. "I think he must be a first year, like us! Isn't it great? Harry Potter here, at Hogwarts!"

"Yes, marvellous," Draco said absent-mindedly, looking up and down the train. "Come on, Crabbe. Goyle. Riddle. He'll be around here somewhere."

I didn't realise it for a while, but looking back on that scene it seems clear to me, if I had been sorted into Slytherin and remained friends with Draco, I may well have become nothing more than one of Draco Malfoy's drones like Crabbe and Goyle. Of course, my feelings for Draco would have been easier to understand and I may not have been so outraged when I discovered who my father is, but I wouldn't be anything like who I am today.

Draco walked down the train like he owned it; considering his father's money, I wouldn't have been surprised if he really did own it. We eventually reached the last carriage, where we found Harry Potter and a ginger boy (Ron Weasley, of course) sitting with a buttload of sweets. I wondered who was more loaded, Draco or Harry.

The conversation clearly didn't go as Draco had planned. It became clear to me, over time, that Draco desperately wanted Harry to be his friend. He just didn't go about it so well, but who can blame him? He was only acting the way he'd been raised to act. He'd assumed his name would impress Harry, that insulting Ron would make Harry realise you just don't make friends with "cretins like Weasley," as he described them on the way back to their carriage.

"The lot of them are morons. Hand-me-down clothes! I don't understand why they have so many children if they can't even afford to clothe them."

Most of the train journey continued like that. Draco ranted on and on about Hufflepuffs, muggle-borns and many other things I don't recall. I wasn't quite sure how I felt about Draco Malfoy. Part of me was disgusted by his bigoted views, but another part of me found him to be quite amusing purely for how long he could talk without taking a breath.

(Many years later, I would ask him why I've never heard him talk so much since that train ride. He said "I talk when I want to impress someone." I don't believe that.)

Eventually the train ride came to an end. We descended onto the platform to be greeted by the largest man I'd ever seen. "Firs'-years!" He bellowed. "Firs'-years, follow me!"

We followed him, hoping he was from the school and not some mad man who came to steal all the first-years, accompanied by Draco's rant about why "that oaf" shouldn't be allowed to work at Hogwarts. I don't remember much about the boat ride across the lake, so I guess it was pretty uneventful. Draco probably ranted. Crabbe and Goyle probably grunted. I probably said nothing. That was pretty much what the friendship would have entailed, had I been sorted differently.

The next thing I can tell you about with certainty is the sorting. Don't worry, all you'll miss is walking and waiting. If this book were to entail everything that happened throughout my life, it would be the size of the Great Hall.

And so the sorting ceremony began. The hat sang its song and Professor McGonagall began calling people up. Some people I recognised from the trail, such as Hermione Granger and Padma Patil (Gryffindor and Ravenclaw respectively). We all got a good laugh when Neville Longbottom (Gryffindor) forgot to take the hat off, and then it was Draco's turn.

"If you're not in Slytherin," he whispered to me, "I don't know you."

"If you're not in Slytherin," I whispered back, "you won't hear the end of it from me."

Sure enough, the hat had barely touched Draco's head before it sorted him into Slytherin. There was a moment of silence and awe, followed by raucous applause, when Harry Potter was called up and sorted into Gryffindor.

The atmosphere of boredom and hunger stayed the same when my name was called, but there were tiny things I never even noticed. McGonagall paused between reading my name and saying it. As I would later be told, terror spread through Rubeus Hagrid's mind. "At firs' I wasn' sure I'd heard righ'," he would tell me much later. "Bu' there was no mistakin' tha' name. Riddle. Nothin' ever surprised me more'n hearin' tha' hat sort ya." Severus Snape was also taken by surprise. He had no idea Suzie Riddle had had a daughter. (He was a smart guy... how it took him two years to do the math is beyond me. Too busy hating Mr Potter, I guess.)

I was never entirely sure what house I wanted to be in. Like many eleven year olds, I had no idea who I was. How was I going to categorise my personality if I didn't even know what my personality was? All I could have told you was that I was quiet unless excited. (That changed over the years, of course.) They don't exactly have a house for that, so I was stumped. I knew one thing, though. After what Draco had said about people from the same family being in the same house, I didn't want to be in Slytherin, not unless it was because the hat saw a Slytherin personality in me.

And so it was that the hat yelled, "GRYFFINDOR!" That certainly changed things.