According to the description of the episode they happened upon a water planet that was starting to fall apart, and so they helped them fix whatever the problem was so it would remain a globe that these people lived on, watery people, I guess, But Paris also discovered that their technology for making oxygen for the people to breathe was polluting the ocean world, so he and one of the people who lived there went and destroyed the oxygen plant -- to save the ocean ... but I assume it would also mean the people would have to leave?