Deck 15 is the cause of a major crisis that StarTrekGuide went through on the first of April last year, and the year before.
We are holding a cadre of Borg on Deck 15. We don't have any way of deporting them without exposing the rest of the ship and crew to extreme risk, so we have to keep that deck locked down at all times, with security teams standing watch at all exits.
The Borg Queen has succeeded twice in breaking out and taking over the ship—and assimilating most of STG's crew—but, obviously, we have prevailed both times.
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