Harry's time at the Burrow soon comes to an end, and he and the Weasleys prepare to return to Hogwarts. Their journey to Platform 9 and 3/4 gets off to a rocky start when George, Fred and Ginny each realise that they forgot to pack something soon after they leave, forcing Arthur to turn the car around and return to the Burrow three times. When they're finally heading for London, they're rushing for time, and Arthur suggests that they fly the car there - he's installed an invisibility booster that'll keep it hidden from the Muggles - but Molly shuts him down. Regardless, they make it to King's Cross with only a few minutes to spare, and head for the hidden gateway to Platform 9 and 3/4. Percy, Fred, George, Ginny and their parents make it through without issue, but when it comes to Harry and Ron's turn, they run towards the gateway, pushing their luggage trolleys in front of them - and crash into the wall between Platforms 9 and 10, the gateway having been sealed off somehow.
After fending off the attention of a nearby guard, Harry and Ron try without success to get through the gateway, and by 11 o'clock - the departure time of the Hogwarts Express - they're still stuck in muggle King's Cross, and Ron brings up the worrying possibility that, if they can't get through the gateway, Mr and Mrs Weasley might not be able to either. The two boys then notice that Hedwig's screeching - she's riding on Harry's luggage, or was a few moments ago - is attracting a lot of unwanted attention, and Harry suggests that they wait by the Weasley's car, which gives Ron an idea: they can fly the car to Hogwarts! Though Harry's reluctant at first, he's quickly persuaded to go along with it when Ron points out that they have to get to school, and that underage wizards are allowed to use magic in the muggle world in "extraordinary circumstances". So they leave King's Cross, load their luggage back into the old Anglia, and after checking that no one's watching, turn the car invisible and take off - where upon they immediately find themselves struggling with the tempremental invisibility booster. They settle for driving the car above the cloud layer and following the direction of the Hogwarts Express.
When they get to Hogwarts, things start go down the sinkhole. First the car runs out of power. Then the boys crash the now out-of-control car into a large willow tree in the school grounds. Then Ron's wand is discovered to have been broken in the crash. Then the tree, of all things, [[WhenTreesAttack tries to smash them into paste]]. Before our heroes can be killed, the car restarts itself, and reverses out of reach of the willow's branches at Harry's urging. Ron barely has time to congratulate the car on this, before the Anglia ejects the boys, their luggage and their pets in rapid succession, and [[ScrewThisImOuttaHere drives off into the forbidden forest]]. Ron sadly remarks that his dad's going to kill him, and a dejected Harry suggests that they head up to the castle.
They arrive at the entrance to the Great Hall just as the school's midway through the sorting ceremony. Peeking through the doors, Harry and Ron make out Ginny as she waits in line to be assigned to one of the Hogwarts Houses, but notice that the grim and thoroughly unpleasant Potions Master Professor Snape isn't at the staff table. The two of them talk possible reasons for his absense - he's ill, he left after failing to get the Defence against the Dark Arts job again, he got sacked - before the man himself - [[RightBehindMe revealed to have been standing behind them for nearly all their conversation]] - explains that he wants to know why they weren't on the Hogwarts Express, and drags them down to his office.
Once there, Snape asks the pair if they were hoping to make a grand entrance with the car. They start to explain, but Snape immediately cuts them off, demanding to know what they did with the car. The boys are initially puzzled by this, before Snape shows them a Daily Prophet article on the car and reveals that, for all their effort with the invisibility booster, [[NiceJobBreakingItHero the car was seen by seven muggles]], in addition to causing considerable damage to "an old and very valuable Whomping Willow". At this, Ron tries to claim that [[CrowningMomentOfFunny the tree did more damage to them]], but Snape cuts him off again, before leaving the office, stating that he's off to fetch the people with the power to expel them.
He returns twice, first with Professor [=McGonagall=], Head of Gryffindor house, and Professor Dumbledore, Headmaster of Hogwarts, and the boys explain their actions to both, before a thoroughly morose Ron offers to get his bags. When [=McGonagall=] demands an explanation, Ron says that she's surely planning on expelling them for this, right? To which Dumbledore replies that they won't be expelled, but he will still make clear to them how serious this is; he'll write to their families tonight, and he'll have no choice but to expel them if they get in any more trouble like this. Snape protests, pointing out that [[JerkassHasAPoint the boys nearly revealed the wizarding world to the muggles]] and [[ArsonMurderAndJaywalking seriously hurt the Whomping Willow]], but Dumbledore states that it's up to [=McGonagall=] to punish the two, since they're both in her house. He and Snape return to the feast, leaving [=McGonagall=] and the boys alone.
After convincing [=McGonagall=] that he's not seriously hurt, Ron enquires about Ginny's sorting. [=McGonagall=] assures him that she's in Gryffindor as well, and starts to talk about their punishment, prompting Harry to argue that she shouldn't deduct house points, on the basis that he and Ron took the car before term started. She assures them that she won't, and settles for giving both of them detentions. Leaving them a magically refilling plate of sandwiches for their dinner, she instructs them to eat in the office and head straight up to the Gryffindor common room when they're finished, before returning to the feast. Ron figures that she doesn't want to convince other students to arrive by flying car.
Once they've eaten, and discussed their lucky escape, Harry and Ron head up to their common room, only to run into a problem at the portrait of the Fat Lady; because of their unorthodox entry, no-one's had a chance to tell them the password to get past her. At that moment, Hermione shows up, sounding more than a bit irked about not seeing them and hearing rumours about them being expelled for crashing a flying car. Her mood doesn't abate when Harry clarifies that they haven't been expelled, but she agrees to tell them the password - Wattlebird - and Harry and Ron enter the common room to an enthusiastic reception from their fellow Gryffindors, all eager to congratulate them for their use of the car.