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.
I noticed you represented Todd Strasser's Fallout and Lauren Oliver's Delirium. I'd keep your verbs here in the present tense. Although differing equally from each other and my own submission, both are geared primarily toward young adults and involve apocalyptic/dystopian fears. While your comp titles are technically different from each other in theme, they're still falling under the post-apoc YA umbrella. Given that your para regarding why you're submitting to this agent is getting a bit long, I'd consider culling this sentence down. Catching the hilarious Go The F*** To Sleep mention, I also figured you had a good sense of humor and would appreciate bemusing or eye-catching titles. That's why I chose you for my submission, LOVE, DEATH, ROBOTS AND ZOMBIES, a 95k-word post-apocalyptic novel straddling the line between YA and adult. Again, your para here is long without having shared anything concerning your own book yet, except the title. Also, hoping the agent will like the title is not terribly relevant because most titles change before being published. Your title is quirky and fun, so let it just be that without saying, "Look - my title is quirky and fun!"
Three factions vie for the scraps of a blighted world -- a race of sentient machines, a mindless horde of undead, and the faltering remnants of humanity. See, this is a great hook - get to it sooner. Fifteen-year old Tristan has no interest in any of it. Living alone in the crumbling library of a long-dead city, his time is spent poaching oversized rats, desalinating water from New Sea, and fiddling with electronics. Tristan is content to leave the world to its struggles. The world, however, does not share his feelings.
Returning to his refuge one night, he's taken at gunpoint by four scouts from the city-state of Foundry. Why do they want him? But what shocks Tristan most is that the girl among them is familiar -- Echo, one of his childhood friends, has survived the destruction of their old village, only to return as an enemy. This sentence is a bit awkward in phrasing. Or so he thinks. In fact, Echo is only doing what's necessary to survive. But that doesn't necessarily mean she's *not* his enemy either, so it's kind of an odd sentence to use as a counterpoint. When she helps Tristan escape, resulting in the death of two of his captors, a desperate struggle ensues with Cabal, the last sadistic scout. Tristan's refuge is burned to the ground while he and Echo take flight into the great American Wasteland. You've put a lot of time into describing this one event / instance in the book.
Homeless, rudderless, the two teens must now put their faith in each other to survive. If Cabal's vengeance doesn't kill them, there's always the radiated wastes, the robots, the roving armies, and the cities full of zombies lurking in their path. Tristan has to wonder: is survival even worth the price? Echo speaks of Haven, a distant enclave whose very name is synonymous with refuge. Third use of the word "refuge" in the query. Yet is it a legitimate escape or just one more humorless joke, one more smiling stab from a merciless world?
This is a well-written query, and the setting is attractive. However, the query is not telling me a lot about what is actually going on in the book. You spend a lot of time on the first para talking about comp titles, then the next is very specifically detailed regarding one event in the book, and the last para gives very broad strokes about a possible destination point that the MC doesn't seem very motivated to reach. I think the query itself would probably raise questions about whether the plot and pacing in the book hold together.
I'm also curious about why the mention of the MC messing with electronics is made, but subsequently dropped. Does this make him valuable? Do the people kidnap him for this purpose? What kind of relationship does he have with Echo? And these zombies and robots sound pretty cool - but why are they there? Just because they're cool? Make sure your world-building elements are present in the query and illustrating that you've painted a believable picture.
Tristan's story is told in first-person. No real need to state this- they'll figure that out once they start reading the sample. I've pasted a short synopsis the synopsis will definitely help establish whether or not the plot and pacing hold together, but some agents don't request a synopsis and might not read the pasted sample. Definitely make sure your query establishes these elements on its own and the first three chapters below, as per the guidelines on your website. I look forward to hearing from you.