Detectives investigate a string of grisly murders around the city.
That’s a fine plot for a game. It covers the basics by providing a clear problem, a potential for action, and a motivation for the players to get involved (they could be the detectives, the vengeful bereaved, or someone who may be next on the list).
Now take that same foreground plot, but let’s provide some context by adding a backdrop plot:
Detectives investigate a string of grisly murders on the eve of a tightly fought Mayoral election.
That’s more like it. Now we’ve got a world that feels more real because things are going on outside the PCs and their mission. It feels less like the whole world just exists to give the players a place to investigate murders. We know what cabbies are talking about, what the news is covering, and what the buzz on the street is like.
What makes a backdrop plot? First of all it has to encompass or surround the characters — if it’s something that has no impact on the here and now it’s just interesting detail, not plot.
Second, it should be clear to the players that their characters are not expected to resolve or even try to resolve the backdrop plot. They couldn’t make a dent in it. It’s literally bigger than the PCs, either because they’re not powerful enough, it’s an unaddressable issue like a social trend, or it’s just outside their jurisdiction or they’re otherwise barred from dealing with it — the superheroes could bust into the courtroom and interfere in the Trial of Dr Null, but it’s understood that such blatant disregard for the law would end their careers. They may interact with it but not fix it.
A backdrop plot can make the world feel more real and establish the tone, the spirit of the times. In addition to adding detail it shows that the PCs are not necessarily the center of the universe — there are things happening that may have nothing to do with the PCs and their adventures.
A good backdrop plot can also add gravity and meaning to even the most mundane foreground plot. Smuggling a package from point A to point B is one thing, but sneaking across the border of two great nations poised for war is another. Do the armies ever even have to show up? No, but the tension is there, and the players feel their characters are part of a larger world.
Agents try to stop extremists from shattering a landmark world peace agreement (foreground) even while shocking news leaks out that probes have found alien microbes in the sands of Mars, the first evidence of extraterrestrial life (backdrop).
Feuding rogues settle scores in the grimy streets of the city of thieves (foreground) but there are rumors that the conquering army of a barbarian king is only a few days away from the city walls (backdrop).
Villagers need protection from raiding goblins (foreground) but they fear their prayers will go unanswered because the prophesied End of Days may now be upon the world (backdrop).
A backdrop plot can also encourage roleplaying and discussion specifically because it isn’t part of the action — the players _can’t_ cure the plague, so all they can do is talk about it and the issues around it as they scurry through the blighted lands. Pick your backdrop plots to emphasize issues or themes you want the players to think about or that highlight or contrast the foreground plot. Normally a plot with all talk could make a boring game, but the foreground plot provides concrete action so the players are not floating adrift in a sea of chat. Like Father, Like Son (Trial of Dr Null) uses this approach to juxtapose the big role-playing issues of the trial of the century and its ramifications on justice and society with the hands-on ‘smack the bad guy’ action of the foreground plot.
Players have a nasty habit of assuming that all things are related: if it’s a detail in the game, it must have something to do with the plot. Does the election have something to do with the murders? It must! Why else would the GM have mentioned it? Put the mirror in your pocket, you’ll need it to get past the bat in the maze of twisty caves, etc.
You may find some players are unnaturally certain the backdrop plot is connected to the foreground plot, no matter how little sense it makes. You know the kind of players I’m talking about. If you want to deflate the insanity here’s a simple solution: put them in situations where they get to explain to NPCs in-character how they think the plots connect. They may settle down once they hear how much they sound like crazed conspiracy theorists (unless of course you are playing a crazed conspiracy theorist character, in which case carry on).
The more personal and climactic the foreground plot, the less you should emphasize backdrop plots. If you are about to finally corner the man who murdered your father, local current events are going to be more distracting than interesting. There’s already plenty of gravity to go around, and the players are probably already heavily invested in the game. A little backdrop can add color (a holy festival spreading cheer through the village even while the characters engage in deadly hunt for their prey), but you don’t need more plot.