
I would have a synopsis written and ready to go before you mail out that query...in fact many agents/publishers ask for it in the initial query package.
A creative writing discussion forum with emphasis on the Mystery Genre.
So, too, the characters we write are multi-faceted. When we write them as such, they all blend one into another, with no personality distinctions. Their physical attributes are different, but you could probably swap around and notice little difference. The most recent rejection letter says, "Your characters are cookie cutter." Of course, in your mind, you (as the writer) see all these "people" as distinct.
Remember the way we describe people? Define your characters the same way. Give your hero two or three traits. That's all. Give him two good and one bad (or two bad and one good, if your character is evil). Lesser characters get fewer traits.
I'm currently working on a piece where my protagonist is gentle (good) and long-suffering in patience (good), but when he's had enough, he's brutal (bad). My antagonist, by necessity is almost the opposite: arrogant (bad) and insecure (bad), which makes him a bully. However, he's eventually willing to admit that he needs the protagonist's help (good).
Most of my stories are character driven, so even though there's a "bad guy" in my story, he's not necessarily the antagonist. In this story, he's a supporting character (they get only two traits, both consistent with which side of the moral question they're on): angry and consuming. I have another supporting character who is friendly and focused.