In 2369, M'ret - now a high ranking Senator - was in danger of being arrested after he spoke out against the repressive policies that were being pursued by the Romulan government. In order for M'ret to escape, Ambassador Spock and the Romulan underground movement arranged for him and two aides to be smuggled out of the Empire so they could defect to the Federation.
To escape, M'ret and his aides were placed in stasis and were transported to the IRW Khazara, then transported to a Corvallen freighter, which would then take them across the Romulan Neutral Zone for a rendezvous with the USS Enterprise-D. In order to arrange for the transport to the Enterprise, Counselor Deanna Troi was captured and asked to pose as a member of the Tal Shiar.
Although the plan went awry when the Corvallens broke the agreement, Troi managed to transport to the Enterprise with the two aides when the starship had arrived to investigate why the Corvallen freighter hadn't arrived. (TNG episode: "Face of the Enemy")
After being revived from stasis, M'ret and his aides were debriefed by Starfleet Intelligence. Amongst the many details that were obtained from M'ret was a detailed map of the aekhhwi'rhoi, the stone-lined sewer systems located below Ki Baratan, and was a hideout for the underground movement. In 2379, Tuvok used these maps to locate Ambassador Spock. (TTN novel: Taking Wing)