Some idea just sprouting out of my mind...
In the sector, an unknown ship has been encountered. Its technology is quite alien, it resists to evey scan, and of course it seems to be heavily armed and shielded. People report having seen it, dead in space, then it disappears at incredible speeds. Those who fired at it were either ignored or utterly destroyed. And sometimes, it is reported to have attacked ships without provocation and depart immediately after their destruction. The reports are so vague about it (it leaves no warp trail of any sort), that the station owners even doubt it exists at all, but some ships have indeed been disapearing and there are some undeniable scans (mainly simple pictures of the ship). They don't even know if there's a single ship or many others. Since they are beginning to be worried, they tried to have the three powers in the station in case the ship attacked.
As for who or what this ship is... I'll let it to you. It could be an automatic probe of a very ancient race, still completing its initial mission, advanced creatures testing the races of the Quadrant, or even ordinary people trapped inside this very advances ship trying to figure out what the various programs in the computer do... or anything else.
Just one crazy idea of mine...
"The main difference between Trekkies and Manchester United fans is that Trekkies never trashed a train carriage. So why are the Trekkies the social outcasts?"
Terry Pratchett