Fred and George Weasley arrive with Ron to save Harry from the Dursleys. They drive the flying Ford Anglia and use it to pull the bars from Harry's window. Using a Muggle trick they've learned, they are able to pick the lock on Harry's bedroom and the cupboard under the stairs to get Harry’s school things.
Fred and George succesfully drive the flying car to The Burrow. They intend to sneak back to bed and pretend that they never left, but they are caught, along with Ron and Harry, by an irate Mrs Weasley.
It is not uncommon to hear small explosions coming from Fred & George’s room at The Burrow.
Fred and George are quick to note the number of Gilderoy Lockhart books on everyone's school shopping list. Fred suggests that the new Defence Against the Dark Arts teacher might be a witch and a fan of Lockhart, while George notes that the books will be expensive.
Fred and George spy on the Slytherin team practising on their new brooms prior to the Gryffindor–Slytherin match, reporting to the rest of the Gryffindor Quidditch team that the seven Slytherin players are no more than greenish blurs while using them.
Fred is alarmed at how panicked Oliver is about the upcoming Quidditch match. He assures Wood they are taking the match seriously, although he remembers Gryffindor's easy victory the last time they played Hufflepuff. After Harry's fall, Fred and George join the rest of the team in the hospital wing. The twins tells Harry what happened after he fell, and that Hufflepuff won the match. They try to cheer him up, and stay positive about Gryffindor's chances of winning the Quidditch Cup.
On the day of the Hogsmeade trip, Fred and George linger around the third-floor corridor by a statue of a humpbacked witch, waiting for Harry. When Harry wonders why they aren't in Hogsmeade, Fred produces a large piece of worn parchment from inside his cloak. The twins tell Harry that the parchment is the secret to their success, and that they have decided to give it to Harry. They tell Harry they found the parchment in Filch's office in their first year. George shows Harry how the map works, and they watch as words and a map appear on the parchment. The twins show Harry the seven passages into Hogsmeade on the map, telling him that Filch knows about four of them. They are convinced they are the only ones who know about the remaining three, although one has caved in. The twins warn Harry to make sure he wipes the map after he uses it, otherwise anyone can read it, then leave the classroom together.
Fred and George attempt to cheer Ron up about losing Scabbers, with little success. The twins, along with the rest of the Quidditch team, are inspired by the presence of the Firebolt at the team practice, and play excellently. They are ecstatic when they win the match against Ravenclaw, and help lead the way to the Gryffindor common room to celebrate.
Fred and George disappear for a few hours during the party, and return laden with bottles of Butterbeer and bags of sweets from Honeydukes. When Angelina questions how they managed to get all the stuff, Fred mutters knowingly to Harry that they managed with a little help from Moony, Wormtail, Padfoot and Prongs.
Fred and George retaliate to the dirty tactics of the Slytherin team during the final. They join the team in a many-armed hug after they win the match, yelling and celebrating as they make their way to the ground. Like the rest of the team, they are carried to the stands by the crowd.
Fred and George arrive at Privet Drive to collect Harry with Arthur and Ron. They offer to fetch Harry's trunk from his bedroom, hoping to get a glimpse of Dudley on their way, as they have heard a lot about him. As the twins prepare to take the Floo Network back to The Burrow, Fred lets a bag of sweets fall out of his pocket - big, fat toffees in brightly coloured wrappers. He scrambles to pick them up, cramming them back into his pocket, then goes back to The Burrow using Floo Powder. George travels back to The Burrow after his twin, carrying Harry's trunk.
As soon as Harry steps out of the fireplace at The Burrow, Fred asks him excitedly whether Dudley ate the sweet he dropped in the living room. He tells Harry that it was a Ton-Tongue Toffee, a sweet that he and George invented. They have been looking for someone to test them on all summer.
Ron tells Harry that Fred and George have been inventing their own joke products, such as fake wands and trick sweets, and were planning to sell them at Hogwarts to make some money. When Mrs Weasley found out their plans, they had a huge row. The twins told Molly that all they want to do is open a joke-shop, and that they don't want to work in the Ministry of Magic like their father.
At the dinner table, Fred and George talk excitedly with Charlie about the Quidditch World Cup final. Fred tells Harry that the 'sample of fertiliser from Norway' that was slipped into Percy's in-tray at work earlier that summer was actually dragon dung, sent by the twins.
Fred and George are annoyed about having to wake up so early for the journey to the Quidditch World Cup, and wish they could Apparate there like Bill, Charlie and Percy. George and Fred are furious when, just before they leave, Mrs Weasley discovers their stash of joke products, which they had been trying to smuggle out of The Burrow. The twins had spent six months developing the sweets.
Fred and George walk with the rest of the group to Stoatshead Hill, where the Portkey to the campsite is located, and where they meet Amos and Cedric Diggory. The twins greet Cedric with a nod, still cross with him for beating Gryffindor in the Quidditch match the previous year. They are visibly irritated when Amos boasts about Cedric's victory in the match. When the Portkey delivers them near to the campsite, Fred and George fall onto the ground, unable to land on their feet.
Fred and George walk to the reserved tent pitches with the rest of the group. They go to collect firewood from the woods with their father when Harry, Ron and Hermione leave to fetch water from the campsite tap.
The twins are introduced to Ludo Bagman by their father when he arrives at their tent. They are eager to make a bet on the outcome of the match, and wager all of their savings (thirty seven Galleons, fifteen Sickles and three Knuts) on Ireland winning the match, but with the Bulgarian Seeker, Krum, catching the Snitch. They also throw in one of their fake wands to Bagman as an incentive, which gives a loud squawk and turns into a rubber chicken. George takes the slip of parchment concerning the bet from Bagman, and tucks it away carefully. The twins are then unable to buy any souvenirs before the match, as they have given Bagman all of their gold.
Fred and George follow the group up the stairs in the Quidditch stadium into the Top Box, where they watch the match between Ireland and Bulgaria. The twins are thrilled when, as they predicted, Ireland win the match despite Krum catching the Snitch. They scramble over the backs of their seats after the Irish team have been presented the Quidditch World Cup and stand grinning in front of Ludo Bagman, their hands outstretched, ready to collect their winnings.
Fred and George are thrilled about winning their bet with Ludo Bagman, and tell their father that they have big plans for the money. They agree not to tell their mother about the wager, as they don't want the money to be confiscated. Fred and George celebrate the Quidditch game with the rest of the group, and go to bed after Ginny falls asleep.
Fred and George are woken by Arthur in the middle of the night. They leave the tents with the rest of the group; Fred grabs Ginny's hand and pulls her towards the woods, followed by George, Harry, Ron and Hermione. The twins and Ginny lose sight of Harry, Ron and Hermione on the way to the woods. They find their way back to the tent after the chaos has died down, shaken but unhurt.
Fred and George are surprised when, after they arrive back at The Burrow, they are enveloped in a tight hug by their mother, who feels guilty at having shouted at them before they left.
On the Sunday before they have to return to Hogwarts, Fred and George are sitting in a corner in the living room at The Burrow, quills out, talking in whispers with their heads bent over a piece of parchment. Fred tells his mother that they are working on homework, although she doesn't believe them. He looks at her, a pained look on his face, and asks her how she would feel if the Hogwarts Express crashed tomorrow knowing that the last thing they'd heard from her was an unfounded accusation; his reference to her greeting after the Quidditch World Cup makes everyone laugh, even Molly.
Fred and George are intrigued when, at Kings Cross Station, Charlie tells them he might be seeing them again sooner than usual. They are irritated when Molly, Bill and Charlie hint that something exciting is happening at Hogwarts this year, but won't reveal what.
Fred and George are thrilled when Dumbledore announces that the Triwizard Tournament is going to be held at Hogwarts that year. Fred tells those at the Gryffindor table that he is going to enter, before hearing that there is to be an age restriction of seventeen. The twins are irritated that, as they will turn seventeen in April, they are prevented from entering by only a few months. Fred stubbornly insists that they won't be able to stop him from entering; he reckons a few drops of Ageing Potion might be able to help them, confident that the impartial judge will go for the best candidates from each school, never mind how old they are.
Fred and George spend their time at breakfast discussing different magical methods of ageing themselves and bluffing their way into the Triwizard Tournament with their friend Lee.
Fred, George and Lee join Harry and Ron at the Gryffindor table after dinner. They tell the boys that they had their lesson with Professor Moody that afternoon, and that they've never had a lesson like it. They are hugely impressed to have a teacher who knows what it is like to be out there, actually fighting the Dark Arts.
Fred and George sit together in the common room during the evening, poring over a piece of parchment. They work silently and secretively. George scratches something out on the parchment with his quill and says quietly to his twin that they have to be careful, as it sounds like they are accusing the person they are writing to. The twins soon roll up the parchment, say goodnight to Harry and go to their dormitory.
Discovered in chapter 15, None
At dinner, Fred and George sit apart from everyone else at the Gryffindor table, and converse in low voices. Ron overhears George saying that if 'he' won't talk to the twins in person they will have to send a letter after all, or they could physically place the letter in 'his' hand themselves. Fred is irritated when Ron interrupts their conversation, and refuses to say who or what the twins were talking about. The twins have been unsuccessful in their efforts to discover how to enter the Triwizard Tournament - George attempted to ask Professor McGonagall during his Transfiguration class how the champions were chosen but was told to shut up and carry on with the lesson.
During one of her rants about the lack of house-elf rights, George asks Hermione whether she has ever actually been into the Hogwarts kitchens. He tells her that he and Fred have been there several times in the past to steal food, and that the house-elves are happy.
Fred is happy to hear that an Age Line is the method of preventing students under the age of seventeen placing their name in the Goblet of Fire, and is certain that the Line will be fooled by an Ageing Potion.
The next day, Fred and George hurry down the staircase with Lee Jordan, having just taken a drop of the Ageing Potion each to become a few months older. The twins ignore Hermione's warning that Dumbledore will have anticipated this kind of trickery; pulling a slip of parchment bearing his name and school, Fred walks right up to the edge of the line and stands there, rocking on his toes like a diver preparing for a fifty-foot drop. For split second after Fred steps over the line their plan appears to have worked, and George leaps over the line after his twin. There is a loud sizzling sound and both twins are hurled out of the golden circle as though thrown by an invisible shot-putter. They land painfully on the ground, ten feet away from the Goblet of Fire. Great long, white beards sprout from their faces with a loud popping sound. The twins join in the laughter of the other students in the Entrance Hall after taking a good look at each other's beards. The twins are sent to the hospital wing by Professor Dumbledore to reverse the effects of the Age Line.
Fred and George greet Harry when he enters the Gryffindor common room; Fred looks half-annoyed and half-impressed as he berates Harry for not telling them he had entered the Tournament. George asks Harry how he managed to enter without gaining a beard as the twins had done.