Fearing that Darvin may be attempting to assassinate Kirk , the crew dress in period uniforms and investigate the Enterprise . They attempt to interact with history as little as possible whilst investigating Darvin . The crew do not initially recognize the Klingons of the time period , and when Worf ( Michael Dorn ) is asked about the difference in appearance , he reply that the matter is not discussed with outsiders ( this is further expanded on in the Star Trek : Enterprise episodes " Affliction " and " Divergence " ) . Doctor Julian Bashir ( Alexander Siddig ) and Chief Miles O 'Brien ( Colm Meaney ) get involved in a bar brawl between the Enterprise crew and a number of Klingons on shore leave . Captain Kirk discipline them on the Enterprise alongside Chief Engineer Montgomery Scott ( James Doohan ) and Ensign Pavel Chekov ( Walter Koenig ) . Bashir and O 'Brien notice that the ship is covered with tribbles . Lieutenant Commander Worf ( Michael Dorn ) and Odo ( René Auberjonois ) trail Darvin as he return to the Defiant . There , Darvin admit that he planted a bomb in a tribble to kill Kirk .