<em>Moaning Myrtle's </em><u><em>sneakers</em></u> light up when she runs.
There are a couple of errors in the sentence. Moaning is an adjective describing a particular Myrtle (one that moans).
Myrtle is the one owning the sneakers. Normally Myrtle would be a noun. It isn't. It's a possessive noun. Myrtle is a possessive and requires an apostrophe.
Douglas to receive manuscript of the tale within 3 days. He refuses to say more until governess manuscript arrives by post in 3 days. The narrator quickly guess the reason why governess has kept the story secret The turn of the screw. Douglas represents the background information before the story. Douglas has sent his men to town to get manuscript.