"We do not live side by side with impurity.
Your civilization is built on abominations. Your galaxy is polluted.
We have come to cleanse it. It is our destiny."
— Warmaster Tsavong Lah

Belkadan, a forested planet in the Outer Rim, is the site of an ExGal-4 listening post, set up to monitor space for signs of extragalactic activity. You're among the scientists and workers stationed there, or perhaps you're delivering supplies, or you've just wandered so far out the edge of the known galaxy; in any case, you are completely unaware that one of the inhabitants of the facility, Yomin Carr, is a Yuuzhan Vong infiltrator sent as an advance agent to prepare the way for his species' imminent invasion.

The beetles he's released into the forest have started emitting noxious fumes, converting the atmosphere to a mix of carbon dioxide, methane and sulfur that kills or mutates all wildlife on the planet. Looks like it's time to run — but he's neither letting you get off-planet nor allowing you to call out for help. He's disabled communications, sabotaged ships and other modes of transportation, and he's even outright chasing and murdering everyone left in the building. Whoops.

Meanwhile, on Sernpidal, something strange is going on. One of its moons is abnormally close — and is moving closer and closer — but nobody else on the planet seems to think it unusual, chalking it up to the ongoing religious festival that celebrates the coming of their goddess. If you're nosy enough, you'll eventually find out that there's a creature holed deep in a crater outside the city center that's pulling the moon into the planet in a spiraling orbit.

Time until impact? Less than seven hours.

The Yuuzhan Vong have been sending scouts all over the galaxy for years, learning about their enemies and their enemies' technology, neutralizing threats, manipulating governments — all to prepare for the arrival of their invasion force at Vector Prime. They're tall, muscular and humanlike, but they have sloping foreheads and are horribly scarred and disfigured (it's a religious thing, don't ask) that they have to use ooglith masquers and cloakers to disguise themselves accordingly. Who's to say your weird cousin or next door neighbor isn't actually an infiltrator?

The wildcard option. You're doing your own thing, wherever you are. So what if the galaxy's at the brink of being invaded by extragalactic aliens with a religious fanaticism and a thirst for war, who glorify pain to the point of masochism, who view mechanical technology as blasphemy, and who can't be sensed in the Force? You have your own troubles to worry about.