The Survivors: Answering a distress call, the Enterprise finds a colony planet nuked but for two survivors.
The Enterprise is answering a distress call from a Federation colony, but finds the colony has been destroyed and the planet ravaged. That's a nice outfit Troi has on there. Although the planet is now barren, their sensors detect a structure with two life forms in it. Troi says she senses something "different" about the life forms. Reeeeeeal helpful.
Riker and an away team beam down in the garden of a nice house. Worf says they don't have any weapons, so Riker goes to knock on the door and is promptly caught in a trap. The elderly couple, Mr and Mrs Uxbridge, who greet them say that some aliens turned up and blew the shit out of the planet. Riker wants to know why the pair were spared, and they go inside the house to look around. Worf admires the old man's gall, and Data is fascinated by a music box. The Uxbridges say they want to remain on the planet, much to everyone's surprise.
While the crew debates what's going on, all Troi can hear is the music from the music box. Don't ya just hate when music gets stuck in your head? Worf says there aren't any Borg or Klingons or so on lurking anywhere in the system, and Picard relates a story about some Andorians who dismantled their spaceship to avoid detection. Troi admits her earworm problem to Picard.
A huge unidentifiable spaceship turns up, shoots at the Enterprise a couple of times causing no damage, and then sods off. The Enterprise gives pursuit, but can't catch up. Picard decides to pop back to the planet. There, he beams down for tea. How civilised.
Crusher tries fruitlessly to treat Troi for her earworm problem.
The Uxbridges ask when the Enterprise is going to leave, and Picard says they need to stick around in case the aliens come back. They insist they're staying on the planet. Could they act any more suspicious?
The alien ship zooms back into the system and knocks out the Enterprise's shields. They fire back to no effect and are forced to retreat as the alien ship assumes an orbit around the planet.
Picard realises Troi's earworm problem is being caused somehow by the Uxbridges. The Enterprise returns to the planet and the alien ship is gone. The Uxbridges are surprised when Picard and Worf turn up in their living room. Despite their protests, Picard says the Enterprise will remain in orbit so long as the pair are alive. Once they return to the Enterprise, the alien ship turns up again and, while Picard instructs the crew to do nothing, the ship destroys the Uxbridge's home. This done, the Enterprise destroys the enemy ship with one photon torpedo.
Though there's no reason left to remain, Picard instructs the Enterprise into high orbit to observe the planet's surface. Picard is smart, the rest of the crew (yes, even Wesley) haven't figured it out yet.
Finally, three hours later, the Uxbridge house reappears. Picard has them beamed onto the bridge and confronts them, revealing Mrs Uxbridge is not real, and Mr Uxbridge is a Q-like life form. Mr Uxbridge removes the earworm from Troi's mind and admits to Picard that after the Husnock nuked the colony and killed his wife, he wiped out all 50 billion of the Husnock race.
The lesson for today is don't nuke people in case one of them turns out to be a superbeing who can wipe out your whole race with a thought.
That's the problem with twist endings - they only work once, then you know what's going on and the crew trying to figure it out is just painful.