On the structure of mysteries in Story Now play, there are really 4 parts to the formula/structure:
* Start out broad and let play winnow results until all other possible conclusions have been eliminated.
Simply put, we start out with set of possible results "a through f." Through interrogation of the mystery, play introduces a number of situations, the resolution of which removes f, then d, then a, then b/c. We're left with e.
* Everyone at the table is handling their responsibilities (GMs bring situations/setting "on-line" via deft deployment of thematically coherent dangers/discoveries while players advocate for their PCs and what they would find to be interesting) but everyone is persisting in a dual state of leading/following for the game pieces they're representing.
This last bit is the cognitive trick to turn that I think most people have trouble conceptualizing until it clicks. Again, as I said elsewhere (and perhaps here), there is a curiosity and an impulsivity that must ride right alongside your attachment. Perhaps it is most similar to that "helicopter parenting" impulse. You have this precious thing that you want to prevent from having bad outcomes...but you have to let go of that to a degree to get there. Suddenly let your child do thing x that gives you anxiety. Be curious if they can do it/about what happens next, but simultaneously be mentally prepared to reassert yourself because you will inevitably have to (if only in degree). You're following/leading at the same time. "Act now, plan later."
* Skillful play should bear out the active winnowing of results to that final conclusion of e.
GMs introduce situations that require players to make moves. Some of these moves trigger action resolution, through which the GM is obliged to change the gamestate and attendant fiction within the constraints of those principles/rules/procedures that govern action resolution. When done deftly, both the actual winnowing of results and the feel of the winnowing of results will yield "the play that got us to these results was skillful."
* Book-keeping, integration, and continuity.
This is pretty straight-forward, but if you're attentively following along and cementing what has come before in your mind, it will result in the care and cognitive horsepower necessary to integrate and maintain continuity.
Most of these things are going to be small-ish (singular session spanning), but if it extends beyond that, don't be afraid to recap, refresh, and talk about it...and have other parties (eg not the GM) doing the recap/refresh to make sure everyone is on the same page as to "how we got here and where we are."
I'm going to deconstruct a quick example of a simple mystery that came into being out of nowhere and was resolved last session in my game with
@darkbard and his wife. All 3 of us were leading and following.
* The Wizard PC wants to repair the Paladin's armor that was ruined in the session before last and possibly enchant it. She wants to deploy a Ritual (a Wizard move), but she needs a master smith or his hammer/anvil, a steel ingot, residuum for the enchant, a successful enchant move. They're at camp 2 of a climb up to a K2esque peak.
She thinks "I believe I've read in my books on the history of this place that there once was a Dwarven Smith nearby." She makes a Spout Lore move w/ Bag of Books augmenting it and gets a 10+ result. I'm obliged to create a Discovery here; something both interesting and useful.
She is leading. I (the GM) am following.
* I create a legend out of whole cloth about a centuries old Dwarven Smith whose Forge was built into the rock off the glacier somewhere not too far from camp 2. His sigil was carved into the very rock which signified the secrete forge's location...but that was many centuries ago and no one has seen him since.
We're now all following. I'm following myself (what I've just made true in the fiction) and they're about to follow it to find the truth of the situation. At this point the reality of the situation is extremely broad. We could winnow to a conclusion of any of "a through f (or more)."
* The set out upon the glacier which obliges me to frame the situation as they follow the details of the legend. Eventually we get to an area of the glacier with meltwater pools and a depression near the northern rock wall that the glacier grinds against. A 10+ Discern Realities move sharpens the picture. Initially we think "this could very well be the site because it looks like some kind of unseen heat may be creating this topographical feature" as hold is spent to ask questions which I'm obliged to answer honestly. Could merely be vents or hot springs. But it could be a forge. But is that forge active signifying life? Is that forge eternally aflame and therefore requires no attendant? Whatever it is, the area is extremely dangerous with multiple hidden crevasse by a thin layer of shifting ice/snow. And the last question is picked and answers the question emphatically; we see the signs of a chiseled sigil into the rock wall, barely peaking out from the top of the massive glacier that has buried it.
This appears to be the place.
Follow > Lead > Follow loop continues for all participants and the mystery starts to peel back, but much remains up in the air.
* A decision-point is navigated. They're either climbing the face (which would be resource-intensive and dangerous) and rappel down to the wall vs trying to navigate the dangerous, unstable crevasse field to the face of the rock wall where the sigil is. They choose the latter.
A move triggers calamity and a snaking crack explodes underneath them and much of the unstable groundcover gives weigh. The Paladin rushes, leaps, and grabs the edge of the collapsed glacier and grabs his understudy Paladin with one arm and pulls her up to safety before he does the same for himself (an 8 on Defy Danger w/ the complication being the threat to his "padawan"...a subsequent 10+ Defy Danger resolves the threat fully).
Unfortunately, his Wizard companion friend did the sort of Act Now, Plan Later impulsive move that she is known for and it got her into big trouble. The failed move meant that the ground swallows her and she immediately begins a horrific tumble as the crevasse swallows her. She is thrown every which way, head over heels and back again as she slams into every manner of jagged, unforgiving ice possible...fully out of control. She slams into the ground with d10 environmental damage, no armor suckitude (this is not great for a Wizard PC and she is nearly killed) and in complete blackness.
We're all following at this point.
The air is thick with electrically charged terror...from what?
Unnerved hesitance leads to "eff it" (Act Now Plan Later) and the Wizard enacts a Light spell...whatever happened here happened long ago...nothing attacks and no signs of life/passage.
The door to the forge is massive...so things much larger than dwarves can pass through (utility or a dwarf's boast in scale of creation)?
The door appears to be "soldered" but not in a precise way...and this was done from the outside and not from the inside?
Still following...still leading...and back again.
I'm time-limited right now so I'm not going to go through all of the rest of it, but suffice to say its a continuation of the same loop of leading > following > leading by all participants, the whole of the process winnowing the fiction to a singular point that answers the mystery "what happened to the dwarf...is the forge still here...who occupies it...what is the story behind all of the answers." So we're at (let's say)
d+g (
@darkbard will know what that means!), arrived their from the initial subset of
a - n, with the
d tying into something that came into play as a "reveal an unwelcome truth" several sessions before but had never been made manifest (I took the opportunity at this point to make it manifest because it struck me as "right" in several different ways, including as an outgrowth of action resolution and to escalate the scene).
The mystery didn't exist 1.5 hours beforehand and even after the initial move that triggered it, none of us knew the reality embedded deep underneath that initial 10+ Spout Lore move. But we each led, we each followed, and we got there.
And it was cool. And it was skillful play by players (tactically, strategically, thematically, Act Now, Plan Later, and Follow and Lead your PC with curiosity about what happens) and appropriate GMing that got us there.
TLDR - Off-the-cuff mysteries are entirely doable. They take practice in terms of craft, habitation of the cognitive framework, and the proper alchemy with respect to table participants.