So, you’ve finally got your campaign rolling; the players are diving into the plot, trying to follow-up on the mysterious death of a local acquaintance involving random power tools and a greater unbound demon. The players have finally found the info on the deceased’s underworld contact, but—what’s this! Isn’t the last name of this black-market fence the same as that of a minor demon lord? Suddenly, the PCs are off investigating this minor cult, under the impression that it’s somehow involved with the murder. The only problem is that the GM hasn’t planned or expected this; it’s all player-driven information.
The average game will involve a lot of on-the-spot improv from the GM, from a number of factors. The chief one being that the players are not the same person as the GM: they all have different views, goals, and perspectives, so no matter what the GM did to set up an event, there are countless red herrings for the players to hook themselves on. Roleplaying games, by nature, are highly flexible organisms with a lot of give-and-take on each side, and players sidetracking themselves into new and interesting plots is a good example.
There’s only three ways you can go with this; two of them involve changing a lot of details. Hence why the art of GM improv is one of the most critical skills for a GM to have.
Option 1 – Keep Going with What You Had Planned
You’ve set up this killer adventure, or bought this awesome module, and had everything perfectly planned out… except that Morphy’s Laws of Combat kicked in, and no plan survives contact with the players. So, plain and simple, you can always just have it lead to finite dead ends, and try to push the game back on target by getting it through to the players that what they’re doing has little or no basis in the plot.
Perhaps the kinder, gentler option is to just tell the players that they’re sidetracked and just circumvent all the in-character roleplaying. That way, they don’t sink a ton of effort and time into something, which becomes frustratingly wasted when they’re told how far from the truth they were.
But if the players are sinking all this time and effort into it, getting really involved, you might want to consider the next two options. It signals that the players are interested in what they’re doing, are being proactive, and deserve some reward (after a good challenge, that is). A lot of Bad GMing I’ve seen falls into the horrible death pit that is the “my game is my story and you cannot deviate from it in a slightest” school of GMing. You’re not rewarding or endearing yourself to the players if you keep telling them to get back on the one true path.
On the flipside, you have spent all this time and effort into designing the adventure, so it’s a personal stylistic choice. If you prefer the GM to wear the big hat, and be the only person wearing the big hat, then stick by your guns; though the more time the PCs spend on the subject, the less fun it’s going to be for them when it turns out to be all for naught.
Option 2 – Roll with the Punches
Well, if where the players are going is more interesting than what I planned, and they’re getting into it, doing Call of Cthulhu levels of research and investigation, maybe I’ll rewrite this on the fly. It really is an evil doomsday cult trying to bring back some minor god, using organized crime as a front, or whatever. The details need not be complex—as long as you can get through the session, you’ll have all week to figure out the rest and retcon the details. This level of proactive player involvement is something I love; the players should be rewarded for this creativity, even if the reward’s “the plot they came up is used somehow.” The best cases of this usually involve player paranoia, but even those are worth playing on.
One GM I know would come up with excuses to wander off and think about what the hell was going on whenever we players came up with something outlandish or unforeseen, usually to save ourselves from being screwed over by someone. Most of the time it would be a bathroom break, or going to get food, or checking on something, but the frequency of his “breaks”—and that they were always around the time when his plans were unraveled—was a dead giveaway.
Improv skills don’t come overnight, and if you’re having real trouble, just tell your players you need ten minutes or so to “read up” on your notes/the adventure. Or just out and out tell them that you need to think about this since it’s not something you originally planned. It may ruin some of the verisimilitude, as well as your GM reputation, but learning takes experience, and experience takes time.
Option 3 – Weave the Players’ Plot into the Game
Probably the best middle ground: take what they’re doing and weave it into what you have planned. Maybe there really is a doomsday cult, but it’ll become the end-boss, and this is just vague foreshadowing for future sessions as it grows in importance and intensity. Or maybe it’s a subplot, something for the players to stumble upon and solve while dealing with the main plot at the same time.
This way, the players don’t completely go off into left field investigating worthless stuff, but it doesn’t take away from whatever you had planned. In fact, nine times out of ten, this is beneficial: the players are handing you an established hook they want to see resolved, especially the more work they put into it; the least you could do is throw them a bone.