Harry watches the Dursleys drive away and then moves his things downstairs, thinking it's strange to be in the house for the last time. Hedwig continues to ignore Harry as he opens up the closet under the stairs, noticing how small it looks. Hearing a roar outside, Harry sees people appear in the backyard, including Hagrid on a giant motorcycle. Ron greets Harry as Mad-Eye Moody, Hermione, Fred, George, Bill, Mr. Weasley, Tonks, Lupin, Fleur, Kingsley, and Mundungus Fletcher file into the kitchen. Tonks gleefully waves her new wedding ring at Harry, but Moody calls them to attention and explains there's been a change of plan.
Revisiting the cupboard under the stairs for the first time in years allows both Harry and the reader to come face to face with how much Harry has grown and changed over the course of the novels. While the cupboard was always a tight squeeze, now, it's unthinkable that Harry could fit there—he's both too large physically, and he's come too far emotionally to put up with that particular kind of abuse anymore.
Since the Ministry can still spy on Harry using his Trace, they're going to break the protection guaranteed by Lily's sacrifice early by moving to one of several secure locations. To throw off any waiting Death Eaters, there will be seven Harrys, thanks to Polyjuice Potion. Harry refuses to let his friends sacrifice for him, and Fred and George tease him for trying to stop this. Moody growls that this is the only way and furiously, Harry pulls out hair and hands it to Moody. Those who will impersonate Harry line up and accept a cup of Polyjuice Potion. After they transform, they change clothes, put on glasses, and grab fake luggage.
Harry has good reason to not want his friends to sacrifice for him—he's lost his parents, Sirius, and Dumbledore because they tried to protect him. However, Harry's anger and unwillingness to let his friends help means that he's not being a good friend himself. Part of being a good friend is respecting others' autonomy to make decisions about this. Further, Harry can't function alone—he needs others to help him accomplish his goals.
Moody barks out who's traveling with whom by broom and thestral. Harry is anxious to learn he'll be riding with Hagrid on the motorcycle, but Moody explains that Voldemort will expect Harry on a broom. In the garden, Harry climbs into the motorcycle's sidecar. Hagrid points out trick buttons as Moody sends everyone off. Within a minute, Harry sees hooded figures shooting spells at him. As Hagrid rolls the bike, Harry drops his broomstick but manages to catch Hedwig's cage. A flash of green light hits her and she falls to the floor of her cage. Harry insists they go back, but Hagrid refuses. Harry starts shooting curses at the Death Eaters.
That Hedwig—an innocent, non-threatening, and caged friend of Harry's—is the first to die reminds the reader that Voldemort and the Death Eaters kill willy-nilly, without any thought for who and why they're killing. It reinforces for Harry that he is going to lose people he loves over the course of this war, and that even the best laid plans can't protect everyone. Regardless, Harry still needs these people in order to simply move through the world.
Hagrid starts pushing buttons and a brick wall erupts from the exhaust pipe. Harry shoots more curses as Hagrid deploys a net and then dragon fire. The acceleration causes the sidecar to start to separate, so Hagrid pulls out his pink umbrella and the sidecar comes entirely apart. Harry levitates the sidecar and finally, Hagrid grabs Harry and throws him onto the back of his seat. Harry lights the falling sidecar on fire and thinks of Hedwig. Harry shoots a jinx at Stan Shunpike and, suddenly, the Death Eaters shout "it's the real one" and disappear.
Remember that Hagrid's umbrella probably contains his broken wand. His unsuccessful attempt to repair the sidecar here exemplifies the consequences of not receiving a complete magical education: he can't do it, and it puts Harry in even more danger. This reads as a cautionary tale, in which the novel suggests that depriving a person of their education can ultimately harm others.
Hagrid uses the dragon fire button again and as they start to descend, Harry sees Voldemort flying without a broom. Hagrid starts a vertical dive and throws himself off the bike onto a Death Eater. Harry can't see from the pain in his scar, but his wand spins of its own accord and shoots golden fire at Voldemort, exploding Voldemort's wand. Harry punches the dragon fire button and knows he's going to crash. Harry stares into Voldemort's eyes before Voldemort suddenly vanishes. The bike crashes into a pond.
The spinning wand is, importantly, something that perplexes both Voldemort and Harry—clearly, there's something that neither of them know about their wands. This sets up one of Harry's quests for knowledge in which he must figure out what exactly is going on with his wand and, in doing so, how to best Voldemort—a quest that Voldemort embarks upon in the reverse.