Anton Chekhov once said:
If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there.
It's a fine rule: a rule of efficiency, a rule that says don't waste a detail and don't introduce a detail for no reason. However, it's a tricky rule to do well.
Chekhov, on the whole, wrote serious and inevitable works. The gun that hangs upon the wall works well in such situations. It is a portent, a threat, a sword of Damocles and other clichés. The audience see the gun and guess that it will be fired. They are filled with fearful foreboding and that is just the sort of feeling that Chekhov liked to fill his audiences with.
However, if, as a writer, you want the element of surprise, then the rule of Chekhov's gun is terribly frustrating. You have to have it there. You can't whip a gun out of nowhere in the last act. But tragic inevitability is only the alias of dull predictability. Of course the bloody gun is going to go off. No tension there.
The writer of the story with a twist is caught between two failings. He must set up the twist: he must give the audience all the information that they need: he must indeed make the twist appear retrospectively inevitable. Yet he must make sure that the audience do not see the twist coming.
A gunless first act would make the shooting of the second unsatisfying. A gunfilled first act must make it predictable.
There are, so far as I can tell, three ways around this.
First, you can introduce the gun and then stick it in a drawer. You pray to all the gods of narrative that people will forget about it until the drawer is reopened in the final scene, at which point they say 'Oh, of course!'.
This can be done, but it's unlikely. The only way, I believe, that it can be carried off is if you then add in a bunch of unnecessary detail into the remainder of the first act in order to confuse them. There is a gun. It is put into a drawer. Then out come the dancing girls, the sword swallower, the talking elephant and the perpetual motion machine. When the gun is removed from the drawer the audience remember that they had forgotten it.
However, this system breaks the Chekhov rule insofar as it requires unnecessary detail. Otherwise don't put it there. What are you now going to do with the dancing girls?
The other method, and the neatest, is the double usage. Suppose that the story is about somebody facing bankruptcy. In the first act the blunderbuss is on the wall. In the second we discover that it is a valuable antique blunderbuss and that in its barrel is hidden a treasure map (if I were writing this we would only realise that after he'd shot himself. But that's because I'm a horrid person).
The gun must fire. That much is inevitable and predictable, but guns can do so much else besides and that, dear tortuous reader, can provide the twist.
N.B. You will no doubt have noticed that I have not provided a single example in this little essay. That's because I don't want to ruin anybody else's twists. I think, I hope, I forlornly pray, that my theory stands up on its own.
The Inky Fool commits suicide