[DS9] Season 3, Episode 20: Improbable Cause
At times this episode can seem to be trying a little too hard with telling us that Garak doesn’t give straight answers, and that the Obsidian Order is cut-throat, but in general Improbable Cause is a good one.
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Read more at Memory Alpha
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Notes:

Odo suspects it might be this guy because the technology used was a common method with his race, and Odo likes racial profiling

Tain is working with the Tal Shiar to attack the founders. He had the former Obsisian Order members killed because he wants to go back to his old job, and they knew too much
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