A missile B'Elanna reprogrammed in the Maquis returns to attack.
Torres discovers that a Cardassian missile she once reprogrammed during her time with the Maquis has been flung across the galaxy and is now heading toward a populated planet. She has to stop it, and the only way to do so is to talk to the weapon itself.
The episode is one of the show's most direct links to the Maquis backstory, and it puts Torres's past directly in front of her. It also asks the crew to take responsibility for the effects of weapons that have been built in the name of a cause. The ticking clock makes it one of the second season's tensest stories.