In the episode, T'Rul has been appointed by the Romulan government as an attache to Starfleet. In exchange for whatever information Starfleet can gather on the Dominion, the Romulans have given them a cloaking device to install aboard Commander Sisko's new ship, the USS Defiant. T'Rul accompanies Sisko and his crew into the Gamma Quadrant on a mission to find the Dominion's leaders, the Founders. Her job on the mission is to operate the cloaking device and to prevent unauthorised persons from interfering with it.
Not Quite Dead...
In "The Search - Part Two", T'Rul and the crew of the Defiant return to Deep Space 9 to find that Starfleet is in the middle of negotiating an alliance between the Dominion and all other Alpha Quadrant powers - excluding the Romulans. This angers T'Rul and she warns that the exclusion of the Romulan Star Empire will mean war.
When Sisko and his officers attempt to steal a runabout so they can collapse the Bajoran wormhole, T'Rul tries to help them, only to be shot in the back by a Jem'Hadar soldier. It is later revealed that Sisko, T'Rul and the others were all plugged into a mental simulation so that the Dominion could determine how much they would sacrifice in order to prevent the Dominion from gaining a foothold in the Alpha Quadrant, and so T'Rul was never actually harmed. She does not make any other appearances throughout the rest of the series.