Dudley Demented

• A certain "skinny, black-haired, bespectacled boy" (1.2) we all know and love is lying underneath the open front window of his aunt and uncle's house on Privet Drive, Little Whinging, Surrey, England.
• It is summer, and the boy (yes, it's Harry Potter) is stuck with his relatives while school (i.e. Hogwarts School for Witchcraft and Wizardry) is out for vacation.
• Harry is lying under this open window because his Aunt Petunia and Uncle Vernon won't let Harry listen to the news.
• But Harry has to listen to the news — he's worried that his nemesis, the evil wizard Lord Voldemort, is going to start going around killing people.
• If Voldemort murders large groups of people, surely even Muggle (non-wizard) news would carry the story?
• But there's nothing unusual on the news.
• So, Harry has no idea what is going on with the war against Voldemort.
• Harry hears a loud crack from the road and draws his wand for self defense.
• Uncle Vernon grabs Harry by the throat through the open window and shouts, "Put — it — away! [...] Now! Before — anyone — sees!" (1.23).
• Harry, Uncle Vernon, and Aunt Petunia all squabble over Harry's magic use, which Uncle Vernon and Aunt Petunia think is perverted and shocking.
• Harry is furious: his relatives continue to be bullying and abusive, none of his friends have been writing to him, and he is totally cut off from the wizarding world.
• At the end of Book Four, Harry saw Voldemort come back to life and murder one of Harry's Hogwarts classmates, Cedric Diggory.
• Now, Harry is stuck by himself, with nothing to do but brood about Voldemort and what he might be doing while Harry is wasting time with his uncle and aunt.
• No wonder Harry is fuming!
• Harry sees his cousin Dudley with a group of his friends.
• Dudley is a stupid, bullying brute.
• Harry is looking for a fight, so he starts laughing at Dudley.
• Dudley mocks Harry for crying out at night: "‛Don't kill Cedric! Don't kill Cedric!' Who's Cedric — your boyfriend?" (1.126).
• Harry is so furious that Dudley dares to laugh about his nightmares and Cedric's death that he pulls his wand on Dudley.
• Dudley suddenly gasps and cries out, "W-what are you d-doing? S-stop it!" (1.141).
• But it's not Harry who is making Dudley feel cold — it's a Dementor, a magical creature that sucks the joy and life out of its victims.
• Harry uses his wand to cast the Patronus spell at the Dementors, and finally, "an enormous silver stag erupted from the tip of Harry's wand; its antlers caught the Dementor in the place where the heart should have been; it was thrown backwards [... and] the Dementor swooped away, bat-like and defeated" (1.173).
• Harry has no idea how a pair of Dementors got to Little Whinging — they're supposed to be acting as guards for Azkaban, the wizard prison.
• Dudley is practically unconscious from excessive Dementor exposure.
• Just then, Mrs. Figg, Harry's elderly neighbor, comes by and shouts something completely unexpected: "Don't put [your wand] away, idiot boy! [...] What if there are more of them around? Oh, I'm going to kill Mundungus Fletcher!" (1.181).