"Treachery, Faith and the Great River" is the 156th episode of the television series Star Trek: Deep Space Nine, the sixth episode of the seventh season. It was first aired on November 4, 1998. The teleplay was written by David Weddle and Bradley Thompson, based on a story by Philip Kim, and directed by Steve Posey.
Odo gets a coded message from Gul Russol and takes off to meet him, even though he considers the possibility that it could be a trap. In fact it is a ploy for Weyoun to meet with Odo and urge him to rebuild the Dominion according to his ideals. Odo distrusts Weyoun, not believing that he would turn his back on the Founders, and the situation takes a turn for the strange when another Weyoun hails their runabout. It transpires that the Weyoun they had come to know for the past few years was recently disintegrated in a transporter accident, and the version currently with Odo (Weyoun VI) is a "defective" clone that does not believe the Founders to be infallible and questions the necessity of the Dominion's war with the Alpha Quadrant powers. His replacement (Weyoun VII) tells Odo that he would be happy to have their runabout destroyed in order to prevent Weyoun VI's secrets from reaching the Federation, even if it means killing Odo. As they try to escape the pursuing Jem'Hadar, Weyoun VI reveals to Odo that an illness is spreading in the Great Link and all the Founders except Odo are dying. Weyoun VII eventually convinces Weyoun VI to commit suicide in order to protect Odo. Before dying, Weyoun VI asks Odo for a blessing.
At about the same time Odo departed, Benjamin Sisko goes to a conference on Bajor, and orders Miles O'Brien to have the gravity fixed on the USS Defiant before his return. Sisko is unconcerned that O'Brien lacks the one crucial piece of equipment required to make the repair. Nog offers to help O'Brien by navigating "the Great River", a Ferengi concept of economics and trade - described as "millions of worlds, all with too much of one and not enough of the other." O'Brien reluctantly gives Nog his authorization code, which Nog uses to make a long series of trades based on rumors, including loaning out Sisko's desk and selling General Martok's prized bloodwine. An increasingly alarmed O'Brien watches with dismay as the young Ferengi works deal after deal; meanwhile, the part he requires appears no closer to arriving.
In the end, Sisko's desk is returned to its proper place; Martok's bloodwine is replaced with an even better vintage, 2309, procured from Nog's cousin Gant; the Defiant is finally repaired; and Sisko himself returns to the station with no idea that it's been anything other than 'business as usual' on DS9. In his quarters, Odo ponders the blessing he gave Weyoun VI.