Need help with a Doppelganger campaign

[Ancalagon]

Now you might think I was trolling there, but hear me out!

Let the players know through vague hints that this will be a doppelganger themed campaign.

There is a town, somewhat isolated, but that trades with others. It's all doppelgangers. They were refugees or whatever, they pretend to be normal, and now they are doing pretty well for themselves. So this wizard moves in, moderately powerful but not an archmage. The locals try to get him to leave (they won't kill him, he's not a bad guy, just not one of them) but the mage doesn't get the hint. He thinks something is wrong.

Through a complicated, finicky test, he manages to discover that *one* towns person is a doppelganger. He calls in outsiders - the heroes - to investigate. They learn that this townperson hasn't been himself lately (due to relationship problems, illness, whatever...) and this confirms the heroes fears. They investigate further and discover that he is corresponding with an orc - a doppelganger agent who's infiltrated the tribe.

The heroes go to confront this fake orc and avert the threat the orc tribe represents. They are victorious. In reality, the doppelganger was in the tribe to make sure the orcs didn't threaten the town, but the players miss it. They find there are more correspondence - more doppelgangers in town!

The towns-doppelgangers realize that the heroes are paranoid about the "doppelganger menace" and create a fake conspiracy for the heroes to discover and twart, sacrificing a few of their members to make it convincing. But alas, they aren't used to subterfuge and while the heroes uncover the fake conspiracy, they aren't convinced that the menace is over.

Once the heroes have exposed too many doppelgangers, there is a great reveal at night. The heroes realize that *everyone is a doppelgangers - the vendors, the farmers, the kids, everyone*. The doppelgangers tell the heroes that they have won, and now that they have been exposed they must flee and scatter to protect themselves. They leave in all directions, leaving the heroes and the dumbfounded wizard behind.

Conclude the campaign by telling the players that this is how, a thousand years ago, the great doppelganger plague was set loose upon the world. Play the last song from bladerunnber by Vangelis.
https://www.youtube.com/watch?v=JAwo7DPUFUM

 

[Ogre Mage]

So as the title implies I am currently in need of help constructing a particular campaign. I am a pretty new DM. I'm struggling with a concept of an investigation / psychological thriller style campaign based around the idea that a town is slowly overrun by Doppelgangers and Mimics being controlled by some kind of hive mind queen or something.

How about a Mind Flayer being at the center of this "hive mind"? It is more powerful than the doppelgangers and crucially, its psionic powers allow it to see through the doppelgangers' shenanigans. The illithid recognizes that it can't infiltrate society because of its monstrous appearance so the doppelgangers are the perfect tools in that regard. The doppelgangers kidnap and replace people who become a steady supply of brains for the illithid. Whether the dopplegangers obey the illithid because they are awed by it or simply out of fear could be an interesting point.

Maybe the mind flayer gets careless and the corpse of one of its victims is discovered, brains missing and all. That would be an interesting curveball to throw into the mix as fears about doppleganger presence are ramping up.

 

[StormCloud 9]

I would make the wizard a dopple the whole time because it would add would make the players question everything they've done, make them even more driven to kill dopples and enforce the dopples role as strong pullers

 

[Imaculata]

Have the mimics replace some of the buildings during the night with mimic-buildings.

 

[Christopher McArthur]

While brainstorming for this campaign I actually got another idea of a specialized mind flayer that kidnaps people and torments them in their dreams. Was gonna have the PCs investigate some missing people reports in a manor / castle, they rescue some hostages, make it back to town, collect an enormous reward, take a rest, and wake up back in the manor / castle. Each time they rest they wake up back in the same place. The things they do in the manor / castle aren't reversed (monsters don't reappear and if they move something it stays there). But each time they keep waking up back in the same room and have to find out how to break the horrific ground hogs day cycle. I might combine the two ideas. Start off with a Doppelganger witch hunt, the party learns of the mind flayer, and then they get trapped in its loop and have to break free. This would solve the issue of a Doppelganger campaign being generic and boring and beef it up to make it meet the length requirement.