As I have been reading submitted materials, I find myself asking this question - How much formula is too much formula?
I've had a slew of queries that could probably have been easily published 20 years ago: well written, good plots, interesting characters. When I thought about why I had to reject them, the same thought keeps coming to mind: "Too standard. Nothing new or exciting."
In a few of them, a body is found in the first chapter (by an innocent bystander), and the police / detective/ sleuth is called in to investigate. One writer had set her book in an out-of-the-way place, and s/he'd provided nice details of the landscape of that no-man's land. Another had a cynical P.I. sitting in his office in the first chapter, doing all those things that cynical P.I.'s do--chomping on a cigar, hurling salacious one-liners at his secretary, commenting on the urban landscape below him.
These type of rejections fall into the "not right for us" category, but the truth is that they're probably not right for anyone because they haven't gone beyond formula. The best mystery writers, I think, are mannerists. They understand the conventions of the genre and implement them, but in a way that causes readers to cock their heads and say "Hmmm." A good writer has to find a way to imbue life into a stock character, whether a little old lady sleuth or a hardboiled detective.
So how do you get your book moving in the first chapter with rushing right into the murder? Maybe you do something that hints at a murder to come or provide an ominous set-up of some sort. Or perhaps you create one set of expectations in Chapter 1, only to dash them at the beginning of Chapter 2 with an immediate plot twist. These are the types of manuscripts that really get my attention, and I would guess the same is true of other editors as well.
I've said it before, but most mass-market mysteries are essentially genre books. Writers have to give the public what they want while also giving publishers a marketing hook. Ask yourself, "Why would someone with limited income buy this book instead of the new James Patterson?" The correct answer would not be, "Because it's better." It would be something like, "James Patterson's villains are always creepy psychopaths. In my book, the psycho's background is more fully explained and s/he is a more fully realized character with as much depth as the protagonist." You get the picture.
If you are hard pressed to explain how your book is different and better, you are likely to face an uphill battle.