DS9 Season 7 Episode 20 The Changing Face of Evil

Plot

The Breen make their alliance with the Dominion known by attacking Starfleet Headquarters in San Francisco. Deep Space Nine's commanding officer, Benjamin Sisko, is concerned for the safety of his wife, Kasidy Yates, a freighter captain. Sisko pulls political strings to get Yates time off from her job; she protests, reminding him that her job is just as important to her as his is to him, and he apologizes and cancels his request. Meanwhile, Damar plots to free Cardassia from Dominion rule.
Dukat persuades Winn to read the Book of the Kosst Amojan, a forbidden text that contains secret information about how to release the Pah-wraiths. Winn's aide Solbor reluctantly brings her the book, but to her surprise, its pages are blank. Suspicious of Winn's interest in evil texts and of her new companion's influence on her, Solbor investigates "Anjohl" and discovers that he is actually Gul Dukat. Winn is horrified to learn the truth about "Anjohl". But when Solbor discovers that they have been trying to release the Pah-wraiths, Winn kills him. His blood drips on the Book of the Kosst Amojan and makes the text visible.
Emboldened by the alliance with the Breen, the Dominion launches an offensive to retake Chin'toka, a star system captured by the Federation some months earlier. In the ensuing battle, the Federation alliance suffers one of its worst defeats of the war. Sisko's ship, the USS Defiant, is among the many ships destroyed by a new weapon unleashed by the Breen: an energy-damping beam that renders weapons and drive systems powerless. The Changeling in command of the Dominion forces allows the survivors to escape, reasoning that their reports will have a demoralizing effect on their comrades.
As the Federation tries to regroup from this devastating loss, Damar releases a public message announcing that Cardassia will revolt against the Dominion; he begins the rebellion by destroying a Vorta cloning facility. Sisko realizes that Damar's rebellion may be the key to defeating the Dominion.