So I've got two choices:
a.) go back to square 1 OR
b.) continue plotting this novel and hope that my brain will be able to handle it. (even though I'm about 99% sure I can't handle it. My brain is slow.)
Sadly, I've got a lot of fun characters planned for this story. I recycled a lot of my old ones that I'd forgotten about (Elsie, Vermeer, and M.D. the Nurse, just to name a few!) and I think I'd have a lot of fun playing with them and re-discovering their quirks. On the other hand, Mysteries are mostly plot-driven, and I pretty much always have more fun while working on a character-driven story.
Therefore, I think I'mma gonna go with option A. Or... at least explore it. If I can't decide on another plot to use, then I might just end up working with my original mystery. At any rate, I'm not just gonna box all my dusty old characters up and stick 'em back in the dusty section of my scull. I bet I can come up with some ways to use them all, regardless of what I ultimately end up doing...