"The Survivors" is one of TNG's most unsung gems — a slowly building sci-fi mystery that thinks big while all the time going to painstaking efforts to keep the drama small and intimate. It starts as the mystery of two people and slowly and implacably marches toward a revelation that's haunting and universe-shaking in its exceptionally quiet way.
The Enterprise races to answer a distress call from the colony at Rana IV; when they arrive, they find the world has been completely destroyed by an unknown alien attack. There are no survivors ... except for Kevin and Rishon Uxbridge (John Anderson and Anne Haney), whose house and a few acres of land have survived the complete scorching of the rest of the planet's surface. Why has this elderly couple survived while the rest of the 11,000 colonists perished?
This story belongs to a subgenre that might best be called "Twilight Zone Trek." Strange things are afoot. The Uxbridges say they do not know why they were spared, but Kevin is obviously hiding something. He's adamant that Picard and the Federation simply leave them alone. An unknown, heavily armed, and mean-looking alien vessel appears and attacks the Enterprise. Its actions are erratic. Troi begins hearing a repeating song in her mind that gets louder and louder and will not go away. Her disturbed mental state starts off as a small, percolating problem, but like the rest of the episode, it slowly and steadily builds until her mental anguish pushes her to insanity.
This story is pitch-perfect in tone. The behavior and method of the attacks from the alien vessel hint that its real goal is simply to coax the Enterprise away from Rana. The clues lead us to the inevitable truth that all of this has to do with Kevin and his pacifist stance when the aliens attacked the colony. Why didn't he fight when the rest of the colony was trying to defend itself? All the answers lie in a revelation that is truly one of TNG's more unsettling concepts: Kevin is actually a superbeing called a Douwd, capable of boundless power, but assuming human identity to live with his human wife Rishon. He put the music in Troi's head to keep her from learning the truth: Great power requires great restraint, which Kevin exercised until Rishon was killed in the attack, at which point he lashed out and killed the Husnock — not just the attackers, but the entire race of 50 billion. Kevin's confession is a stunning revelation of frightening power, profound individual guilt, and audacious sci-fi imagination. If you stop and think about a being with cosmic power like that, humanity seems but a speck of insignificance.
For once, there's no humanistic preaching that Picard can possibly make. Concerning a being of such limitless power, Picard simply concludes, "We are not qualified to be your judge." The episode ends with one of Picard's most memorable voice-over logs: "We leave behind a being of extraordinary power and conscience. I'm not sure whether he should be praised or condemned — only that he should be left alone."