B'Elanna is split into Klingon and human halves by the Vidiians.
B'Elanna Torres is captured by the Vidiians, who split her into two separate people, one fully Klingon and the other fully human, as part of their search for a cure to the phage. The human half must find a way to help rescue the other while the crew works against the clock.
The story is one of the show's most important episodes for Torres, because it lets her face the part of her heritage she has always struggled with. It continues the Vidiian storyline and shows that the species is more than a monster of the week, with real desperation behind its actions.