Harry Potter and all characters, etc. belong to J.K. Rowling, not me.
There are two main concepts to consider before reading this story. One is that missing one single red light can save a few minutes on a car trip, thus changing the arrival time to be earlier.
The second is that the way Mrs. Weasley was practically shouting, "Attention all muggles, we're going to Platform Nine and Three-Quarters," while Harry was looking for a way to get to that destination seems too much of a coincidence. The goal for all magical people at Kings Cross should be to protect the Statute of Secrecy, so openly speaking about muggles and the unusual platform would obviously be forbidden.
Therefore, I conclude that Dumbledore put her up to it, knowing that Hagrid had failed to instruct Harry on how to board the train. Whether it was Albus trying to make up for a simple mistake by his large friend or because he was the most evil manipulator in history is for other stories to explore. This one is simply hypothesizing what would've happened if Vernon had run one red light and arrived a few minutes earlier.
Without further ado, I present…
One Traffic Light
"Vernon, the light is red!" shouted Petunia as her husband ignored that fact, barely avoiding a collision with a white station wagon. As he swerved out of the way, he couldn't hear his wife's rebuke over the horns that were being blasted at him. Dudley squealed in terror.
"Sorry, Pet," he finally managed to say, once they were across the intersection. "I guess I'm in a bit too much of a hurry to be rid of the freak," he chuckled.
"But you don't have to kill us all," she replied. "Are you all right, Dudley-poo?"
"Harry laughed at me," he complained loudly.
"How dare you!" hissed Petunia as she glared at her nephew.
"I didn't say anything at all," Harry defended, "although, now that you mention it, that squeal did match his tail…"
Petunia looked ready to slap Harry, but he was saved by Vernon announcing, "We're here," as he parked the car. It was 10:25 a.m. He dumped Harry's trunk onto a cart and wheeled it into the station for him. Harry thought this was strangely kind until Uncle Vernon stopped dead, facing the platforms with a nasty grin on his face.
"Well, there you are, boy. Platform nine – platform ten. Your platform should be somewhere in the middle, but they don't seem to have built it yet, do they?"
He was quite right, of course. There was a big plastic number nine over one platform and a big plastic number ten over the one next to it, and in the middle, nothing at all.
"Have a good term," said Uncle Vernon with an even nastier smile. He left without another word. Before Harry could turn to watch the Dursleys drive away, he noticed a timid boy that appeared to be his own age pushing a cart with a woman that, judging by her age, was probably his grandmother.
The boy had a trunk similar to Harry's on the cart his was pushing, and a toad was sticking its head out of his shirt pocket. Harry sighed with relief as he remembered that toads were specifically listed as acceptable pets for Hogwarts students. The woman looked far too imposing to speak to, not to mention weird. Harry figured that all magical adults dressed weirdly in the muggle world, but he'd have never imaged someone wearing a vulture-hat.
"H-h-how do you know I won't just run into the wall, Gran?" asked the boy, appearing terrified.
"Shhh," his grandmother replied, "We don't want to be overheard." She then pulled the boy to an empty corner and Harry snuck closer to hear the explanation, doing his best not to be noticed. He was successful, because the woman told her grandson, "Neville, it's simple. You just run toward the wall between Platforms nine and ten and you'll find yourself right in front of the train. Now, go on."
The boy obeyed, looking extremely frightened as he ran toward the wall, and disappeared. The older woman than walked through and Harry followed. He didn't see the group of redheads that were just arriving.
"…packed with Muggles, of course," Molly Weasley announced as loudly as she thought she could get away with as she looked around. Dumbledore had told her that Harry Potter had raven black hair and would be wearing oversized clothes and taped glasses. "Now, what's the platform number?" she asked, hoping that, wherever he was, Harry would overhear.
Her youngest child and only daughter piped in, "Nine and three quarters!" She was holding her mother's hand as they walked her brothers toward the correct area. "Mum, can't I go…"
"You're not old enough, Ginny, now be quiet. We're here…" she looked around, hoping to spot the child she was asked to help, "…at Platform nine and three quarters!" She hoped she hadn't said that last part too loudly in her desperation to find the boy. She had.
"Excuse me, ma'am," said a man who walked up to her wearing a pair of pink swimming trunks, a black turtleneck sweater with a bowtie tied sideways over the collar, and a mink coat. She had a hard time not laughing at the obvious wizard. At least her husband had some idea how to dress in the muggle world. "I'm Auror Dawlish, and I'm afraid that I'll have to give you a ticket for violating the Statute of Secrecy…"
"Boys, go onto the platform. Ginny, stay here," she interrupted the Auror, who wasn't very pleased about that.
"Would you like to add a month in Azkaban to your penalty?"
"No, sir," she replied, now giving the man her full attention. She didn't notice what her daughter was doing.
Ginevra Weasley watched her brothers all cross over to Platform nine and three quarters while the mean Auror was talking to her mother. She glanced at the pair to see that Molly Weasley wasn't even looking in her direction, so the ten year old girl ran toward the wall between Platforms nine and ten, passing through it and finding herself looking at the Hogwarts Express, just like she'd done every September and June, not to mention most Decembers and Januarys, for as long as she could remember. The only difference was that now her mum wasn't holding her hand.
She glanced around for her brothers, but couldn't see any except for the twins, Fred and George, who were busy with their friend Lee Jordan, who appeared to be showing them a large spider. "I'll bet that would make Ron wet his pants," she whispered to herself as she quickly made her way to the train and boarded it for the first time.
Her first instinct was to sit in one of the compartments and try to blend in, but then she remembered how her brother Percy had bragged that as a prefect, he'd be one of the people patrolling the train. He may be a pompous fool, but he would recognize his own sister and get her in trouble. Therefore, she went about finding a place to hide.
With that in mind, she quickly made her way toward the back of the train. She speedily ducked down when she spotted her brother Ron talking animatedly to a boy with black hair and glasses, sneaking past that compartment and, thankfully, not being spotted. Just a few compartments down, she spotted one that appeared empty except for a few trunks on the racks above with an old black blanket beside them. She figured that someone had already claimed the compartment and would be returning any second. With some difficulty, she climbed up on top of the luggage rack as the train whistle blew, grabbed the blanket, wrapped it around herself, and did her best to make it look like she wasn't hiding there.
The door to her compartment opened at virtually the same moment the train started moving. She gripped the rack from under the blanket to avoid rolling down as she listened to the boys who were sitting down. She was sweating by the second under the thick covering.
"We're serious, Lee," laughed a voice that was very familiar to Ginny.
"Our mum's probably been arrested by now," said the same voice from a different location. Ginny silently groaned as she realized that, of all the compartments she could've picked, she ended up choosing the one where Fred and George were sitting.
"And she calls us troublemakers!" both twins declared before they, along with Lee, burst out laughing. Suddenly, Ginny heard a small metallic clang.
"Crap!" shouted Lee Jordan. "I was laughing so hard I dropped my tarantula's cage. It's getting out! Catch it!"
Ginny held the blanket tight around her and closed her eyes, hoping the loose spider wouldn't find her. She listened to various expressions of frustration over failing to catch the loose pet.
"It's on the luggage rack," exclaimed Lee. "On top of the blanket."
Come to think of it, Ginny did feel something beginning to crawl on top of her…something much larger than a normal spider. Now, unlike her brother Ron, she did not have a specific phobia regarding arachnids, but, given the circumstances, nobody could criticize her for letting out a large scream while rolling around in an effort to knock the spider off her blanket.
"Ginny?" exclaimed both her brothers at once.
"Busted," she muttered sadly before the twin pranksters of Hogwarts started laughing uncontrollably. She got angry. "It isn't that funny!" she shouted while tossing the blanket at them.
"Oh, yes it is, Little Sis," said Fred.
"It's a wonderful prank on mum!" proclaimed George.
"We're so proud!" they said together.
"We've got to make sure," added Fred.
"That you can stay," finished George.
"Won't she just be sent home?" asked Lee.
"Maybe not," the twins answered together and continued to explain in Twin-speak.
"Hogwarts rule 56 A states…"
"…once a child has been sorted, they are officially a student."
"Rule 63 C says…"
"Once a student has been removed from Hogwarts for any reason…"
"They cannot return."
"If we can get you sorted."
"Mum and dad can't remove you,"
"Unless they don't want you to attend Hogwarts," they finished together.
"How do you know all the rules?" asked Ginny skeptically.
"We memorized them in first year," answered George.
"In hopes of breaking them all," completed Fred.
"Now," George stated thoughtfully, "how to get you past Percy…"
"And Ron," added Fred. "I'll bet he'd turn her in."
"He doesn't want her in his year," George proclaimed.
"Imagine having one of your siblings in class with you," Fred asked with fake trepidation.
"The horror!" they stated together in mock terror while Lee and Ginny laughed.
Jordan suggested, "The first thing she'll need is a Hogwarts robe."
They spent the rest of the trip doing things like putting a mild notice-me-not charm on her face so that nobody would recognize her, as well as plan for her sorting.
"First years!" shouted the largest man Ginevra Molly Weasley had ever seen. She knew, of course, that he was Rubeus Hagrid, the groundskeeper, and that she was to follow him, staying as far away from Ron as possible. He led them to a small dock. "No more than four to a boat," he instructed. Ginny got onto one of the last available ones with a few girls she didn't know.
"Hi," said one of the girls in her boat. This one had red hair like Ginny's. "My name's Susan Bones."
"Ginny," she replied, not knowing who might know about her family. Her dad did work at the Ministry, after all. She decided to change the subject before she was asked her last name. "I've been looking forward to this my whole life."
"Me, too," replied another girl in the boat. This one had pretty blonde hair. "My name's Lavender Brown."
"I'm Lisa Turpin," said the fourth girl, her long dark hair blowing in the wind. "I didn't catch your last name."
At that moment, the boat turned and they were all treated to an incredible sight. Hogwarts castle looked absolutely glorious from this vantage point. "Wow," said Ginny, not having to fake her awe. The other girls stayed silent as well, absorbing the view in front of them. When they arrived at the shore, Hagrid knocked on the door and introduced them to Professor McGonagall, who gave them a speech about the four houses that they would be sorted into, before leaving them alone outside the Great Hall.
"So," Ginny asked her companions, while keeping her voice down so Ron, who was still with the black-haired boy he'd sat with on the train, wouldn't recognize it, "which house do you want to be in?"
"My family's all been Hufflepuffs," declared Susan, "so that's the house I want to go in. I know what most people say about that house, but I for one think loyalty and hard work are quite important."
"I'm hoping for Ravenclaw," said Lisa, before shyly adding, "I've always been a bit of a bookworm."
"I don't care which house I get in," announced Lavender with a grin, "as long as there are cute boys in it." This comment earned her some giggles from the other girls.
At about that moment, they were interrupted by a few ghosts, who, after realizing that the gathered children were new students, welcomed them to Hogwarts just before Professor McGonagall returned to escort them inside.
"This will be the year, Gred,"
"It sure will, Forge,"
"We'll earn detentions before the opening feast even begins!" the Weasley twins declared proudly as they watched the first-years led into the hall. Both had their wands out and under the table they were seated at.
Lee Jordan had a hard time not bursting out laughing at his best friends' antics. He was sitting between them and the teachers, so that none of them would notice the spells the twins were about to cast.
The sorting began with a girl named Hannah Abbot going into Hufflepuff, followed soon after by Susan Bones. The twins waited until everyone was looking at the new celebrity, Harry Potter, being sorted. The sorting hat stayed on his head a bit longer than most of the kids, but eventually, it declared him to be a, "GRYFFINDOR!"
While almost every eye in the Great Hall watched Harry Potter make his way to the appropriate table, Fred and George Weasley both shot a spell at the Slytherin table. The first spell changed its color to hot pink while the second caused it to start dancing on its four legs to absent music. The Slytherins all jumped back from their now animated pink table in confusion while the professors looked around to find the culprit. Professor Snape narrowed his eyes at the Weasley twins, who were laughing louder than everyone else.
The moment the table started to dance, Ginny ran for the stool with the Sorting hat, ignoring her new friends who suggested she should stay with them, and put the old blue hat on her head. It wound up covering her eyes.
"Well," said a voice inside Ginny's head. "What do we have here? Aren't you a bit too young to start Hogwarts."
"Please don't tell," she begged the hat.
"Ah, I see. You snuck onto the train. A very Slytherin thing to do."
"I like to think it was Gryffindor courage," she argued silently.
"I should probably tell the Headmaster that you don't belong here."
"Please don't. I've wanted to…"
"I said that I should, not that I will. It's not my concern if the professors don't count the students that they sort. Better be…
"GRYFFINDOR!" was shouted loudly enough that everybody heard it, even Professor Snape, who had just assigned Ginny's co-conspirators a detention after undoing their Spellwork on the Slytherin table. She ignored everybody's stares (they were shocked someone got sorted before her name was called) as she walked straight to the Gryffindor table and sat next to Ron's new friend – the Harry Potter.
"I'm Ginny," she said to boy while her youngest brother watched her from the group of unsorted students, too shocked to speak.
"I'm Harry. It's good to meet you."
At that moment, the doors of the Great Hall burst open, revealing a panicking set of red-haired adults. Molly had been escorted to the Ministry by Auror Dawlish and spent half the day in a holding cell. The self-important ministry employee had ignored her pleas for him to check on her youngest daughter, simply because he thought she didn't show him the proper respect. Once she was released, she found her husband in his department at the Ministry and they began searching Kings Cross Station, as well as the Burrow (in case Ginny had managed to find her way home) and were now going to look for her at Hogwarts, on the odd chance that she managed to board the train.
Molly Weasley took in the sight – her daughter with a smug look in her face sitting at the Gryffindor table while Fred and George were being yelled at by Professor Snape, while Ron was waiting to be sorted.
"Ginevra Molly Weasley," she shouted. "You are in sooooo much trouble!"
As much fun as it would be to write the inevitable howlers that would come to Ginny and the Twins, as well as the other repercussions, I have no plans of continuing this story at this time. However, I may change my mind in the future…
If a few paragraphs toward the beginning seem familiar, that's because I borrowed a few scenes at the station from JKR.