The Breen have entered the war, and they hit the Federation where it hurts: Earth. What's worse, they have developed a new weapon that drains all energy from a ship, and not even the trusty Defiant can withstand it. On Bajor, Kai Winn finally completes her FaceHeelTurn, while on Cardassia, Legate Damar does something that even the Founders never saw coming.
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!This episode contains examples of:

* AbandonShip: The crew of the ''Defiant'' is forced to do this before she's destroyed.
* BloodMagic: How the Text of the Kosst Amojan is revealed.
* CurbStompBattle: One of the worst the Federation suffers in the war.
* EnemyMine: The Federation isn't exactly friendly with the Cardassian Union, but at this point they'll take any help they can get.
* FaceHeelTurn: Kai Winn. Granted, she was never quite a good guy to begin with, but this episode makes it official.
* HeelFaceTurn: Legate Damar has finally had enough.
* LaResistance: This episode is the beginning of the Cardassian uprising.
* MonumentalDamage: The Golden Gate
* OneHitKill: The ''Defiant'' of all ships is fried in one hit.
* PowerNullifier: The Breen's energy dampening weapon.
* SinkTheLifeboats: Weyoun suggests doing it to the Federation Alliance, but the female changeling overrules him.
* TomeOfEldritchLore: The Book of the Kosst Amojan, which Winn and Dukat need to release the Pah-Wraiths.
* TheWorfEffect: The ''Defiant'' bites it to show that the Breen mean business. Of course, [[TropeNamer Worf]] ''is'' on the bridge when it happens...