* The Laws of Planning
2) Go with the players' plans.
2a) The amount of time spent on a plan should give it proportional
importance to the plot.
2b) Red herrings should be used sparingly, so they don't stink up the
place.
Go with the players' plans.
There's a GM truism that the game is about the PCs, not the NPCs. This actually has several levels to it and is worth repeating a few times, not because every GM has a favourite NPC, but because the story IS about the PCs... and that's something to consider when you are collectively writing it.
This is a corollary to the idea that there's more than one way to skin a cat. If the players have come up with a game plan, well, there you are. Except for details, that's what you have to use.
Let's go back to that big black door I was mentioning earlier. One of the things I did wrong in that game (the second iteration, at least) was that after the players spent so long trying to get through the door, I didn't want them to get through it like that, so I wasted their gaming time. That was their plan. If I wanted to have something punitive happen, that's time for another plot twist, not to take out on the players, which is what wasting gaming time is.
(At least in that situation; there are people who feel diversions and outside talk during gaming is wasteful, I consider it personal character and group development.)