The Long Night (Star Trek Deep Space Nine, No 14)

Centuries ago, the Supreme Ruler of the planet Jibet fled a democratic uprising, taking with him many priceless works of art. Now Quark's greed leads Commander Sisko and his crew to the lost treasures -- and to the Supreme Ruler himself, preserved in cryogenic suspension.
The discovery sparks unrest on Jibet, and launches an alien armada against Deep Space Nine â„¢. As Dr. Bashir struggles to keep the dying ruler alive, Jake and Nog uncover deadly evidence of lingering Cardassian treachery. Now, Sisko must somehow keep the mysteries of the past from destroying all hope for DS9's future.