The Adventure Seed
Self-replicating, planet killing warships made by a long dead race to kill all other intelligent life are assaulting the various humanities. The noble houses back in the Innner Sphere and Core have opted to hide behind a "defense grid", leaving the Rim to its fate. The PCs are vigilantes who have stumbled on a cache of technology from the time of the Imperium - a power which had achieved dominion over all of known space before it fell into decadence and decline. At their height their technology was more powerful than anything available nowadays, and thus it is particularly useful against the Planet Killers. This is the edge you were looking for. So with the stakes in mind you set out to kill the Planet Killers and show the cowards behind the Grid up.