I diagree with brad's opinion that this story "jumped the shark" with the bird/plane/Voldemort chapter.
This chapter has a lot of the Dr. T magic, and I don't see it as derivative. One of the major themes of the story so far has been that the Wizarding world needs to have better appreciation and respect for the Muggle world. The portkeying onto an airplane wing certainly demonstrates that point, dramatically.
Another way in which the story maintains much of the Dr. T magic is the careful description of features that a less serious story would skip over. Here, Dr. T is once again providing details that a mere humor piece would never cover. The careful discussion of the Sirius/Lucius co-operation is a good example of this. Also, Dr. T shows good creativity in attributing a strong motive to Sirius's attempt to kill Snape.
Dr. T, you write: "it would take decades before the book was successfully renounced." Unless the author himself renounces the book, it can't really be "renounced", can it? I think there's a good word that would do it; the best alternatives I can come up with is "before the book's arguments were successfully refuted", or repudiated.
Dr. T., you also write: "as if he could care less". You usually have your stories' narration avoid solecisms, so I assume you meant "as if he couldn't care less".