The Defiant crew travels back in time to the events of The Trouble with Tribbles.
Two agents of the Department of Temporal Investigations question Sisko about a recent Defiant mission. Returning from Cardassia with the recovered Orb of Time, the ship picked up a human trader who was really Arne Darvin, the Klingon spy Kirk unmasked a century earlier. Darvin used the Orb to send the Defiant back to Space Station K-7 and the original Enterprise, intending to kill Kirk with a bomb hidden inside a tribble.
In period uniforms, the crew searches the Enterprise and the station, with Bashir, O'Brien, Worf and Odo caught up in the famous bar brawl with the Klingons. Sisko and Dax trace the bomb to the grain compartments, where it is beamed into space, and Sisko takes a moment to meet Kirk before the Orb brings them home. Made for the franchise's 30th anniversary, the episode inserts the cast into footage from The Trouble with Tribbles, and the DTI agents let Sisko off with a warning.