Yeah, it's a pretty infamous episode of voyager, Some even consider it the worst episode of the entire Star Trek genera.
Basically Tuvoc and Neelix got merged in a transporter accident. The rest of the episode was about the morality of returning the 2 to their original bodies which meant the death of Tuvix. Or let Tuvix live, but it meant Tuvoc and Neelix would be dead. Most on the ship stood with Tuvix, but in the end Capt. Janeway made a bastard move and forced them to return Tuvoc and Neelix y reversing the transporter accident. .