In 2368, the Romulan Tal Shiar, led by Commander Valerius, made an incursion into the Itarian nebula, well within Federation space where they planted the wreckage of a D'deridex-class warbird along with a series of warp dampeners, to lure out T'Uerell, a Vulcan scientist responsible for the destruction of a world within the Romulan Star Empire, who Romulan intelligence had reported as being in the sector. At the same time, the prototype USS Defiant was sent to the Itarian nebula, which was to serve as a proving ground for the Defiant's trial run, because of its isolation from prying eyes. Once the wrecked warbird was discovered by the Defiant, the warbird was destroyed by the Tal Shiar and a confrontation ensued, resulting in the Defiant being captured and taken to a Romulan starbase that had been established within the nebula, but not before sending a report back to Starfleet.
Soon after, a task force of four Starfleet vessels, led by the USS Enterprise-D, were sent into the Itarian nebula in response to the Defiant's report. By destroying the warp dampeners, the Starfleet vessels were able to restore warp capabilities and found that the Defiant crew had been held captive aboard the Romulan starbase. Taking out the starbase's shields, an away team was beamed aboard to retrieve the crew, who were then transported to the Defiant. Ultimately, the Starfleet vessels successfully fought through the Tal Shiar and were able to escape the nebula, detecting an old Vulcan ship along the way. (ST video game: Legacy)