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.
* InsistentTerminology: It's not a ''toy''; it's a ''model'' of the Alamo.
* LaResistance: This episode is the beginning of the Cardassian uprising.
* MonumentalDamage: The Golden Gate Bridge.
* MyGodWhatHaveIDone: When Winn learns that she's been consorting with Dukat, she looks like she's about to throw up.
* OhCrap: The ''Defiant'' crew's reaction to the Breen weapon. As well as to the attack on Earth.
** The Dominion's reaction to Damar's rebellion. Weyoun, in particular, knowing that he's the last clone.
* 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.
* WhatTheHellHero: Cassidy chews Sisko out for getting her taken off the active list.
* TheWorfEffect: The ''Defiant'' bites it to show that the Breen mean business. Of course, [[TropeNamer Worf]] ''is'' on the bridge when it happens...