A lethal Romulan-trained agent turns against her paymasters in order to prevent them from unleashing a terrifying biological holocaust. Admiral Uhura of Starfleet Intelligence sends the young Romulan to investigate with a team of special operatives: Dr Beverley Crusher (Star Trek: The Next Generation), a young Lieutenant Benjamin Sisko (Star Trek: Deep Space Nine) and the Vulcan Lieutenant Tuvok (Star Trek: Voyager).