Meet my Hatchet of Death (or, some other colorful description RC Lewis and I come up with at any given moment). This is how I edit myself, it is how I edit others. If you think you want to play with me and my hatchet, shoot us an email.
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.
If you're looking for query advice, but are slightly intimidated by my claws, blade, or just my rolling googly-eyes, check out the query critique boards over at AgentQueryConnect. This is where I got my start, with advice from people smarter than me. Don't be afraid to ask for help with the most critical first step of your writing journey - the query. My comments appear in green.
London, 1867, a city of ghosts, werebeasts, and magic gangs. Meh. You need something stronger here. This is your hook. Work location and time in somewhere else, thread it into a sentence. Those without magic are pawns and targets, and Wayward Collins—a man with no magic, money, or power—has built his entire life around staying hidden and neutral. After months of work (some of it legal, some not), he’s almost ready to start a new life far away from the city and its magic. But when an unguarded moment leads to disaster, Wayward’s compulsive need to protect himself has tragic consequences and a young girl is savagely killed. This is very vague. We don't know what the actual plot here is, just that something bad happens.
Enter Lord Cadogan, the wizard who witnessed the event, you definitely need to get specific about the event - otherwise motivation remains a question mark and, wanting a safe, non-magical servant, blackmails Wayward into taking the position. Wayward might not have any innate magical talent but he has enough arcane knowledge to be useful, and Cadogan enjoys having a dogsbody valet forced to bow to his every whim. But events take a serious and bloody turn weren't they already if someone was savagely killed? when one of Cadogan’s footmen is murdered by magical means and your sentence construction uses a lot of and throughout. Either pare down the sentences or rephrase - an agent will think that the novel will have the same issues , affronted at the threat to his household, Cadogan drags Wayward into his hunt for satisfaction.
Haunted by his previous mistake and loathing every second of his enforced servitude, Wayward is determined to remain uncooperative. But each step of the investigation stirs up further trouble; the dead footman had his own secrets, a demon attack hints that other magical factions might be interested, and one police inspector just won’t leave the matter alone. Suddenly there's a lot of elements being thrown in here. Even Cadogan might not be the arrogant braggart that Wayward initially expected. As matters come to a head, Wayward is forced to reconsider his plans for the future. Why? What plans? Back to the get out of town plans? Before, all he wanted was to leave the city far behind. But Wayward’s one mistake has changed everything, and now the city isn’t willing to let him go.
Vagueness is a lot of what isn't working here. We know that bad things happen, and that people have secrets, etc., but we have no idea what those things are or how they tie together. An agent can't get any idea of motivations, or if there's a compelling plot at work within the novel because the query is full of allusions only.