Anyone who's read mysteries (or romances, or thrillers, or even horror novels) for any length of time quickly finds out that there is a "formula" (or pattern, if you prefer) to all books in the genre.
In other words, the same scenario, same type of protagonist, same type of complications, all appear in every cozy with the names and places changed. After a while, I find that a lot of series all begin to sound the same ("I thought the protagonist's name was Jessie...? Oh, wait, that's the other series I read, the one where the girl moved back to her hometown after being dumped by her fiance and started her own pet massage business! This is the one where the girl dumps her philandering husband and moves away from her hometown to start an organic pet treats business!")
In the mystery genre, and I'm talking cozy mysteries, since that's what I write, there are a few "ingredients" that appear to be standard across the spectrum. When I decided to write my Black Horse Campground series, it was tempting to completely defy convention and ignore all the formulas until it occurred to me: these formulas exist because readers LIKE them. When they pick up a cozy, they expect the story to go a certain way--the protagonist has to find acceptance in her new life or business, she must have a painful past (romantic or otherwise) to overcome, she must find a new romantic interest (usually a love triangle results,) and, of course, she must face opposition from the local law enforcement when she takes on the task of solving the mystery.
That still doesn't mean that an author can take a template and use the "find and replace" tool to write a story.
Here's how I "tweaked" the formula to make the Black Horse Campground series a little different from all the other cozies.
1. Location--Corrie Black, my protagonist, has a painful past (more on that in a minute) but she didn't leave her hometown to escape it, or even come back to her hometown. She's always been in Bonney County, working her family business.
2. That painful past--not only does Corrie nurse a broken heart from a breakup many years earlier, she still remains friends and interacts on a daily basis with her ex, who happens to be....
3. The oppositional (did I just invent a new word???) local law enforcement--Sheriff Rick Sutton who has been one of Corrie's best friends since childhood, her first (and only?) love, and one side of...
4. The love triangle--in which both of the protagonist's love interests have legitimate reasons for not jumping into a relationship--Rick is a divorced Catholic and J.D. is a recent widower--but both are situations that could change. And I don't intend to drag it out until everyone (including myself!) is ready to give up on it!
Of course, many elements remain the same. The protagonist usually has a close friend to discuss the case with, there's always some character to provide light comic relief, another character who adds complications. It's up to the writer to add some spice, zest, and sweetness to their own recipe for a cozy and make it truly their own!
Just add murder....