I'm not looking for an argument this morning (my time), but I'm noticing there's a difference between us--especially also thinking about your post just upthread about running a mystery scenario for your family.
I've said (and I maintain) that I'm not a big fan of ratiocination-type mysteries in TRPGs, for a few reasons, but I don't think that setting up a relatively traditional mystery (who killed the merchant?) is more than framing the fiction, while you seem to consider it on the lines of a railroad if the players can't decide, e.g., who killed the merchant, as opposed to figuring it out (or not figuring it out, or being wrong).
I guess you would think that the solution to the mystery (who killed the merchant?) would best not be decided by the GM, at least not beforehand (maybe as the result of an action resolution the gave them that responsibility)?
One connotation of the word
railroading is that there will be multiple pre-determined scenes. In the murder mystery I described that's not quite the case, although it's fairly close to that: there's the inspection of the staterooms, the interviews with the handful of salient NPCs, etc. But unlike (say) the famous Dragonlance modules there's no story development. The situation is essentially static and the players "poke" at it with their PCs and extract information from the GM.
So (i) it lacks the motion or dynamism that might be connoted by
railroad, and (ii) it doesn't really involve a "living, breathing world" and so in some ways is closer to classic map-and-key exploration (in my game I achieved this result by setting it on one level of a starship in jump space - so no one getting on or off - with only a handful of characters, more than half of whom were played by the players).
The whole thing was a big puzzle, and so in that sense it's all about GM agency. As I think I posted upthread, there was one point where the GM agency really came to the fore: when the PCs interviewed one of the conspirators. We were no using any mechanics, and so I just had to play her responses - but I am not an actor, and the players made it clear that they weren't sure what to make of the way I portrayed her: was it
my bad acting, or was I portraying
her bad acting/lying, or something else? That moment of play certainly involved deliberate GM manipulation of the situation in this sense: for reasons entirely to do with pacing and satisfactory resolution, I wanted to keep this NPC a viable suspect but not to have her crack under pressure.
Whether that counts as
railroading isn't something I want to die in a ditch over. But in a game experience with overall low player agency, that was probably the moment at which it was lowest.
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On the bigger picture about mysteries: to me it depends in part on what the point of play is. The episode I've just described was one where the players came into it knowing it would be a murder mystery, because that's what my daughter wanted.
In my Prince Valiant game I ran the Episode from the Episode Book called the Blue Cloak. This has a mystery to it, in the sense that one of the NPCs turns out to be a ghost. Here's the actual play write-up (the three PCs are Sir Gerran, Sir Justin and Sir Morgath):
As they were getting close to Warwick, and travelling in the dark still looking for a place sheltered enough to camp without a tent, they came across a weary old man in a blue cloak. (The scenario in the Episode Book is called The Blue Cloak.) A merchant, he had been set upon by bandits who had taken his mule and his goods. He knew the game trail they had travelled down, and asked the PCs to help him. Being noble knights, of course they agreed to do so! As they travelled through the woods and down the trail, he asked about their families - learning that one was the son-in-law of the Duke of York ("What an honour to be aided by such a noble knight"), and that the other was returning to Warwick to woo the Lady Violette - and told them of his own daughter and son-in-law living in Warwick. Then, as they could hear the lusty singing of the bandits at their camp, he asked the PCs to go on without him as he was too weary to continue. The PCs were a little suspicious (as were their players) but opposed checks of his fellowship vs their Presences (even with bonus dice for suspicion) confirmed his sincerity.
The PCs approached the camp, and Sir Gerran drew his sword and called on the bandits to surrender. Their leader - wearing a very similar blue cloak to that of the merchant - was cowed, as was one other, but the third threw a clay bottle at Sir Gerran (to no effect) and then charged him sword drawn (and gaining a bonus die for knowing the lie of the land in the darkness), only to be knocked almost senseless with a single blow, resulting in his surrender also ("When I insulted you, it was the wine talking!").
The wise woman and old man, who had been waiting up the trail with the merchant, then arrived at the camp to say that the merchant had (literally) disappeared! Which caused some confusion, but they decided to sleep on it. The next morning, in the daylight, they could see that the brooch holding the bandit leader's cloak closed was identical to that which the merchant had worn. Sir Justin suggested he no doubt had multiples of his favourite cloak and fitting, but Sir Morgath had a different idea - "When you left the merchant you robbed, was he dead?" His presence roll was a poor one, and the bandits answers that the merchant fell from his mule and hit his head and died, and that they had buried him and had intended to place a cross on his grave first thing in the morning. Sir Morgath doubted this - "You didn't give him a proper burial - his ghost came to us last night!" - and I allowed a second presence check with a bonus but it still failed, and the bandits simply muttered protestations of innocence under their breaths.
Sir Justin received a vision from St Sigobert, and by plunging his dagger into the ground at the head of the grave was able to sanctify the ground. A cross was then placed there, and the group returned to Warwick with their bandit prisoners and returned the merchant's goods to his daughter.
In this episode of play, there is first an extended period of framing and free back-and-forth narration: meeting the merchant, agreeing to help him, coming upon the lustily-singing bandits.
Then there is an action declaration - Presence vs Fellowship (in Apocalypse World this might be
read a person or
read a charged situation) - which does not produce any additional insight into the mystery: the framing remains essentially unchanged.
Then there is some more framing - the bandits and the cloak - and action declarations, to cow and beat down the bandits. These succeed.
Then there is yet more framing, established via narration from two NPCs (the old man and the wise woman) - the merchant has disappeared, it's morning, not only is there a duplicate cloak but it has a duplicate broach.
This finally leads to more action declaration: the bandits are interrogated but don't confess, there is the vision - I don't remember now whether there was a check of some sort, or if it was free GM narration, but my best guess would be that it was some sort of Presence check - and then the sanctification of the ground (that was probably "say 'yes'" following a check for the vision).
The return to Warwick is freely-narrated denouement.
By looking at the action declarations we can see what was the point of play: defeating the bandits and trying to get them to confess, and sanctifying their hasty burial of the merchant. There are no exploration-oriented action declarations aimed at solving the mystery. All the information needed to solve the mystery is provided in the framing exposition.
How might the situation have resolved differently, had some of the checks been different? The bandits might have confessed and been taken on as servants by the PCs. The ground might not have been sanctified and so a haunting of the PCs could have continued or perhaps their conversion of the wise woman from paganism (which had happened earlier in the same session) might have been undone. What is at stake is not
the mystery as such but these relationships between the PCs, the NPCs, their faith, etc.