We all know the first line of a query is your "hook." I call the last line the "sinker." You want it to punch them in the face, in a nice, friendly kind of way that makes them unable to forget you after having read the 300 other queries in their inbox.
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Sixteen year-old high-society girl Gwendolyn Darling is only trying to keep the delightfully dull Humphrey Redford—and marriage—at bay. Interesting. Not a bad hook although 16 seems very young for marriage. It makes me wonder the time setting of the novel, and I'm not seeing that indicated elsewhere in the query either. A hint wouldn't hurt. And to her pleasant surprise, it seems to be working fairly well. So what if she has to miss out on parties, balls, and social events of the year by pretending she’s sick? It is well worth the cause. It is also how Gwen ends up alive instead of dead like her parents on the disastrous night of the Jolly Roger ship malfunction. Raises the question of what kind of illness she's faking since it sounds long term? Also, does "malfunction" work in this sentence? I feel like a ship "wrecks." "Malfunction" makes me think of an amusement park ride... but maybe that's what this is? A little bit more of a hint (or different word choice) could clarify easily.
With only her brother to comfort her, Gwen mourns the death of her parents when she starts hearing whispers, rumors… I'd cut the ellipses use and work with full sentences here because it could raise style questions about the ms itself - unless that is in keeping with the style of the ms. There is gossip going around that the Jolly Roger accident wasn’t an accident… Which means, maybe, just maybe, her parents aren’t dead after all. Wait... why? If it wasn't an accident then I would assume instead that it was maliciously intended... not that the supposed victims were actually alive. Hopeful and intrigued, Gwen begins an investigation of her own.
And it turns out she’s not the only one curious about that night.
With the help of her new acquaintances, adventurous Miss Penelope Panberly and her friends (plus one mechanical crocodile), Gwen embarks on a mission to find out what actually happened on the night of her parents’ “death”. Period goes inside quotations. Also what's the story with Humphrey? He's fallen off the map. You're doing a good job of getting the voice and snark in here with the names and voice, though.
Because too many strange things have been happening, and stranger things are happening still. There are reports of dangerous shadows coming to life, attacking people; girls are disappearing—not to mention Gwen’s constant run-ins with a too-dashing-for-his-own-good thief, which may be the strangest thing yet…. This just took a turn. We went from slightly snarky upper-class mystery to paranormal, disappearing girls, and a thief?
Is it Bernard Clifton? The only survivor of the Jolly Roger accident? Is it the thief, whose criminal behaviors raise eyebrows? Gwen must find out who is responsible before she herself is kidnapped. Because, it’s for certain: whoever it is, they are not stopping and they will do anything to stop her.
I'm definitely confused about what your genre would be on this. The voice of the query starts out light and offbeat humor with mystery, then there's a paranormal element tossed in, that honestly, I think is going to be a turn off. Then we veer back into mystery elements with the closing "Whodunit" para. I'm also confused about motivations. Why is Gwen even running into this thief? What is he stealing? Where is he stealing these things and why are they crossing paths? How does he fit into the story? How does the element of missing girls have anything to do with the accident? Why does the MC feel that she's being targeted? Your voice and writing in this query is decent, but you'll need to draw lines between all these different plot points to illustrate how they're a cohesive whole.