Today’s second glitch:
Don’t dangle your participles — it’s rude. 🙂
I see this a lot, though, and it may be the reason why some Writing Gurus(tm) say it’s grammatically incorrect (even though it isn’t) to begin a sentence with an –ing word. (It’s easier for them to say, “Never do this!” than to say, “This is how to do it correctly.” Mercenary Proofreader is still somewhat annoyed that, a couple of decades ago, he had to teach his art students about grammar because their English teachers weren’t up to the task.)
The way the first sentence is written, it implies that the unusual item was bought by the several people who have been stalking and threatening you. *shakes head* I’m certain that’s not what the writer meant to say, so let’s clarify it.
After you buy an unusual item at a charity shop, numerous people begin stalking and threatening you. One day you find a secret compartment in the item which houses something you have to protect at all costs.
Compartments are in things, not on them.
You’ll also notice that I tightened the predicate (verb plus any objects, complements, or adverbial modifiers — yes, adverbial, because anything that modifies a verb is functioning as an adverb, even if you choose to be grammatically incorrect and use an adjective instead so you can pretend you’re not using adverbs), because there’s no reason to separate stalking and threatening when they have the same object: you.