Faces

A brilliant episode, which like the best sci-fi explores profoundly human concerns. B'Elanna Torres is captured by a species that is affected by a debilitating disease simply called 'The Phage'. The believe that her Klingon DNA might be the solution to their problems. To test that theory, they split up B'Elanna into two people - one Klingon, one Human, giving them somewhat distinct personalities. Both of them are then forced to examine who they are, and how much both 'faces' of B'Elanna go into making her the distinct person that she is.

The plot is also a good excuse to change how Klingon B'Elanna looked. The prominent Klingon forehead from the beginning of the season is replaced by a less severe version. Possibly, the start of the romance between her and Paris too, though he gets into a messy love triangle with Kes the next season.