B'Elanna's past catches up to her when Voyager encounters a Cardassian missile speeding through space in the Delta Quadrant.
Years ago, when she and Chakotay were members of the Maquis fighting the Cardassians, the Maquis got hold of a Cardassian missile and on her own initiative she reprogrammed it to strike Cardassian territory. The weapon was launched and never heard from it again; it was thought to be destroyed. Voyager chances upon it here on the other side of the galaxy, and it is headed directly for a populated planet called Rakosa V. It must be stopped; millions of lives are at stake.
B'Elanna is struck with horror at the thought of her deception wiping out a civilization and she vows to stop Dreadnought at any cost. Meanwhile, the disgruntled Maquis Michael Jonas betrays Voyager′s crew by informing the Kazon of the situation. B'Elanna beams onto Dreadnought′s control deck to try to shut it down. This is a tough task, since she had originally armed the missile with a sophisticated battery of countermeasures to make it invincible. B'Elanna is accused of tampering with Dreadnought and working for the Cardassians. Dreadnought then lies to B'Elanna and she returns to the ship. She realizes she must find a loophole in her own plans in order to persuade the missile that it should stand down from its plan of attack. She engages in a match of wits against herself (Dreadnought was reprogrammed to speak with B'Elanna's voice, reflecting just some of the alterations B'Elanna herself had made to its programming) to stop the threat before it is too late. Captain Janeway is willing to destroy Voyager to save the millions of people on the planet. At the last minute B'Elanna cuts through Dreadnought's power core with a phaser and Voyager beams her out, banking away from the planet as the missile explodes.