Harry heads up to his room where he finds a weird creature bouncing on his bed. The little guy says he's a house-elf named Dobby. Um, okay.
Dobby tells Harry that he's got a message for him but it's kind of tough for him to explain. When Harry suggests he sits down, Dobby bursts into really loud tears. See, a wizard has never treated him like an equal.
Guess you must have met some pretty jerky wizards, Harry tells him.
Yup, Dobby says, and then he freaks out again and starts banging his head on Harry's dresser.
Harry gets Dobby to stop slamming his head and the house-elf explains that he had to punish himself because he almost said something bad about the wizard family he serves. Turns out Dobby has to serve one wizard family forever and they definitely do not know he's here on Privet Drive talking to Harry Potter.
But Dobby has to come and warn Harry—he can't go back to Hogwarts. Bad stuff is going to happen this year. There's a plot. It's all very ominous and vague.
Then Dobby starts hitting himself with a lamp again.
Uncle Vernon comes upstairs because of all the noise and Harry just manages to shove Dobby into his closet in time.
After Uncle Vernon leaves Dobby also reveals that he was the one who stole all the letters that Harry's friends have been writing him this summer. Gee, thanks Dobby.
When Harry tries to get them back, Dobby runs out of the Harry's room and downstairs to the kitchen. There, he spots a cake Aunt Petunia made just sitting on the counter.
Dobby tries to get Harry to promise he won't go back to Hogwarts, but Harry won't do it. The kid is a boy of his word.
So Dobby snaps his fingers and levitates the cake into the living room, dropping it right on Mrs. Mason's head.
Naturally, the Dursleys assume Harry is responsible.
And we're guessing Uncle Vernon didn't get that big business deal after all.