I’m picturing this being more of a cyberpunk adventure hook, but I’m sure it could be adopted to pretty much any genre or setting.
A large biker gang of Native Americans (from all sorts of tribes) have banded together and decided they will retake what was once properly theirs. They plan on reclaiming the entirety of North America. Their plans are broad and sweeping, but not all that well thought out. Unfortunately, the PCs are smack in the middle of the initial uprising and must either decide to join the biker gang or fight them. Unfortunately, the biker gang will only take someone with at least 1/8th Native American blood in them. They have a small lab setup and some scientists doing tests on DNA samples from volunteers to ensure this is the case. Anyone that volunteers to join, but does not pass the DNA test, is given a pass for 24 hours to leave the immediate area because of their good will toward the biker gang.
What will the PCs do against a relatively large and very well armed gang? Run? Fight? Join? Hide? Lots of fun options there.