Ep 15. By Inferno's Light

In "By Inferno's Light," the fifthteenth episode of the fifth season of Star Trek: Deep Space Nine, the Dominion has taken control of Deep Space Nine, with the help of the Cardassians. Sisko and his crew are trapped on a Dominion ship that is heading towards a strategic target in the Alpha Quadrant. Meanwhile, Gowron has declared martial law on the Klingon Empire, and Worf must navigate dangerous political waters to save his people.

The episode begins with the crew of Deep Space Nine gathering at a memorial service for Jadzia Dax, who was killed in the previous episode. Sisko is visibly shaken by her death, and vows to avenge her. The scene then shifts to the Dominion-controlled Deep Space Nine, where Odo is being interrogated by the Female Changeling. She wants to know why Odo has not undergone the "morphogenic virus" that would make him a loyal member of the Dominion.

On board the Dominion ship, Sisko and his crew are being held prisoner. They are joined by Garak, who was also captured by the Dominion. Garak reveals that he has been working with the Obsidian Order, the Cardassian intelligence agency, to sabotage the Dominion's war effort. Sisko decides that the best way to fight back against the Dominion is to destroy their ship, but he needs Garak's expertise to do it.

Meanwhile, on Qo'noS, the Klingon homeworld, Worf is summoned to the High Council. Gowron has declared martial law, and is using the opportunity to consolidate his power. Worf is suspicious of Gowron's motives, and realizes that the Klingon Empire is in danger of tearing itself apart. He decides to take matters into his own hands, and sets out to convince the other Houses to join him in opposing Gowron.

Back on the Dominion ship, Sisko and Garak work together to destabilize the ship. They manage to create a power surge that disables the Dominion's weapons, but they are quickly discovered and captured. The Jem'Hadar, the Dominion's genetically-engineered soldiers, attempt to execute Sisko and Garak, but they are saved at the last minute by a group of Klingons who have boarded the ship.

The Klingons are there to take revenge on the Jem'Hadar for killing their comrades. Sisko and Garak use the distraction to seize control of the ship, and set a course for Deep Space Nine. The Klingons agree to help them get there, but only if they can get their hands on a cloaking device that the Dominion has in their possession.

Worf arrives on Deep Space Nine just as the Dominion ship is approaching. He confronts Gowron, and challenges him to a battle to the death. The two engage in a brutal fight, with Worf emerging victorious. He then assumes the position of Chancellor of the Klingon Empire, and pledges to lead his people back to glory.

The episode ends with Sisko and his crew returning to Deep Space Nine, which is now free of Dominion control. Odo is cured of the morphogenic virus, and agrees to work with the Federation to fight the Dominion. The stage is set for the final conflict between the Dominion and the Alpha Quadrant powers.