I'm not completely convinced about the separation between 'solving a mystery' and 'telling the story of solving a mystery' as usefully distinct terms. At least not to do the definitional work its being asked to do in this case. I wouldn't, for example, suggest that Call of Cthulhu, in some of its adventures, somehow isn't about telling the story of solving a mystery, nor would I say that Brindlewood Bay isn't about solving a mystery.
To throw a third ingredient into the pot here, I think I'd probably say that Monster of the Week represents emergent gameplay but also retains the 'specificity of the mystery = X' that BBay sometimes confuses people about. Is MOtW 'solving a mystery' or 'telling the story of solving a mystery'. IDK, the terms don't seem to add much. Perhaps others have a nuanced view of the two terms, I'm not sure.
My suspicion is that the nature of BBay mechanic has led people to try and describe it as 'not really about solving a mystery' and this in turn leads to trying to define what it might be if it's not that. I think that the difference between emergent and prepped play (or whatever term you prefer) covers the difference between CoC and BBay without the need to split the Gordian Knot of 'what is a mystery, anyway'.
Brindlewood Bay gets a lot of press for trying something new for the whole investigation mystery process. I think it fails utterly to deliver on both. But the idea they were onto did spawn what does work = and that came from
Apocalypse Keys.
ApocKeys went away from "letting the dice decide the truth" of the mystery, back towards "the GM decided the truth when they made the mystery", but they let the
"we found a clue" be organic instead of planted by the GM. This solves problems while retaining the process of a mystery uncovery.
Now the
GM need only focus on the mystery its self, and then when a CLUE pops up, they can look at their mystery aspects and
define the clue at that point in time and place and circumstance. No
more very very frustrating "well, i never thought a clue would be in a breadbox" or
"i had to spend three weeks guessing where players might look for clues" or
"i didnt know that the sailor talking about pudding was a clue" = so awful and frustrating and game breaking and exhausting!!
Once the players have enough CLUEs they can
roleplay to discuss their clues, and then
roll to address the mystery. on
success, the
GM tells them where to go based on their discussion roleplay so they can confront the mystery and they are prepared. on
fail, its the same but the mystery has the upper hand. on
fumble, the mystery gets away with some of it and can't be 100% resolved. on
critical success the characters are prepared and have a bonus to aid them in the confrontation.
It's all still GM mystery ideas, its all still part of their plot. No dice roll just blurts out "yeah, i guess that lame idea was right" like BB does.
You still have to roleplay to find out what happened and to resolve it (final battle, race for time, escape in time, whatever the mystery finale is)
To me, this means that we there are very strong differences in how mechanics drive emergent gameplay - and its those mechanics that drive me away from D&D and towards other games. And not all of those other games get it right either...