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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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The Adventures of Rita Homez capitalize (or italicize) your title is Holmes and Watson as multicultural, thirteen-year-old girls in modern San Francisco minus the deerstalker hat and the magnifying glass. It's a middle grade, first-person narrative that's around 30,000 words with 60 comic-style illustrations. Normally I think it's better to jump in with a great hook and your ms specs at the end of a query, but honestly your concept is so fascinating, it's perfect up front. Also you might want to specify if you do the illustrations yourself.
Eric is one of the best surfers in California at age 13? Or is he just he best young surfer? but every time he hits the waves of Ocean Beach, he gets attacked by a shark. Nobody else is attracting Jaws, just him, which is what catches his friend Rita's attention.
It just so happened tense problem here - your earlier para is present, this one slips to past that Jane, Rita's new foster sister, unplugged the computer and dragged Rita out of their house on Baker Beach just in time to see Eric get attacked. And even though Rita's a junk-food-eating, video-gaming zombie who hardly ever leaves her room, nobody is better at figuring out something this crazy. Definitely do some re-arranging here - you've got Eric already being attacked and Rita being aware of it in the first para, and now we're seeing her view it for the first time. You can easily pare down and jam these two paras together for flow and simplicity. I see now that your tense issue actually agrees with this chain of events, but you need to have the query in all one tense.
Also, I'd dump the "Also" for flow Rita knows that if Eric gives up surfing, he'll spend all of his time hanging around her with that goofy smile on his face which will just drive her nuts. She and Jane need to get that boy back in the water and fast. Nice gesture to Holmesian anti-social tendencies going on here. There's a big surf competition coming up this Saturday and plenty of people in town don't want Eric to compete. Top of the list is Devon, a fourteen-year-old millionaire who designs custom surfboards and his sidekick, Irene, the most popular girl in the seventh-grade. There's also the Grays, a spooky father and son team who run the oldest surf shop in the Bay Area and are famous for surfing the frigid waters without wetsuits. Nice - you've got a good mix of supporting characters in your cast here and are showing it.
But for some crazy reason, Rita's convinced that getting her dorky friend Lenny, I'd use dashes here instead of commas who thinks he's a wizard, ready for a magic show will bust the case right open. Jane may not agree with Rita's wacko methods, but they both know that Eric's either on someone's hit list or he's just naturally tasty. And if they don't come up with an answer, he could end up a shark treat at this Saturday's competition!
This is a solid idea for many reasons - you're riding the wave (see what I did there?) of Sherlockian popularity and answering a very definite call for more diverse literature for youth. Get this query streamlined - you can do some condensing and the tense issue needs addressed - and then get this out there in the New Year!