The year is 1789. For context's sake, it is a few years before the French people will start singing about whether other people hear them singing and a little bit after those across the pond demonstrated their dislike of tea by throwing it into said pond. So, as you can tell, it was a time of great revolutionary fervour.
The place is France. No need for context here, I assume you know where France is.
Old timey French society was split into three estates: the First Estate was the clergy, the Second Estate was the nobility, and the Third Estate was everyone else - you know, the people, the good guys.
Now, King Louis XVI didn't want the Estates to mingle. So he did what any self-respecting ruler of a country would do when he doesn't want something to happen: he locked the door. That's right! He snuck into the building in the middle of the night clad only in his bedclothes, pulled out an ornate golden key from a chain around his neck, locked the door, and gleefully sprinted away. (Sources are inconclusive as to whether these specific events actually occurred, but historians do agree that the door was, indeed, locked).
When the Estates General arrived at the meeting hall the next day, they were angered by this underhanded trick! The following conversation likely took place, but in French:
"The door is locked! We can't get in!"
"How can we have a revolution if the door is locked?"
"Does anyone have a key?"
"I didn't bring my key! Who would have expected the door to be locked?"
At this point, everyone was probably beginning to panic. That is until our hero, we'll call him Pierre Jean-Luc Baguette, bravely stepped forward and said something like:
"Well, if we're not meeting, I guess I'll go. I have a tennis game in an hour."
The crowd gasped. Baguette had a membership to the neighbouring indoor tennis court! They had a place to meet after all! Baguette secured guest passes for all of them and it was there, on the tennis court, that the Estates General swore and signed The Tennis Court Oath. The Oath declared that their meeting would not disband until a constitution had been written.
The King nearly lost his head when he heard the news (too soon?). But a week later, he gave in. The People: 15. Louis: love.