In Purgatory’s Shadow / By Inferno’s Light (S5, E14 / E15)
Okay, perhaps I’m cheating, sticking these season five episodes together, but this two-parter brings to a head so many narrative threads, including the Klingon conflict established in ‘The Way of the Warrior’. It was another game changer of an episode that set up the galactic war which would begin at the end of the season.
Worf and Garak attempt to locate a Cardassian signal deep in Dominion space and find themselves prisoners on an internment camp. But it’s their fellow prisoners that spark the biggest twists; Enabran Tain, who is revealed once and for all to be Garak’s father, and Dr. Julian Bashir, wearing the old style uniform that hadn’t been seen on the show for several episodes. The reveal that Bashir had been *replaced by a Changeling* for several episodes was one of the series’ biggest twists and raised the stakes further. The ending to ‘By Purgatory’s Shadow’ as hundreds of The Jem’Hadar poured through the wormhole was one of the best cliffhangers the show ever did.
What’s so great is that ‘By Inferno’s Light’ doesn’t let up, starting with another huge twist as quasi-ally Gul Dukat reveals his true villainy and sells Cardassia to the Dominion as an ‘ally’ all for a seat at the table. In just one episode, the Klingons are driven back from Cardassian borders, reforging the Khitomer Accords and the stage is set for the Dominion War to come.