GAH! It could not have been a better fit for me if it had been written for me personally!
The movie opens with 50 people in a dark space, each standing on a lighted circle. If they move off that light or touch each other, a loud warning sound blasts. If they stay off their light, they die.
Even if everyone does everything right, every two minutes, one of them is killed.
After a few deaths, they learn more and more about how the person is chosen to be killed. They vote on who dies. Every two minutes, they have to vote. It's a secret vote though (done with technology -- small twitches of their hands), so no one knows who the others are voting for. The next hour and change is all about how people act, what makes them turn on each other, how personalities come out, all sorts of plotting and planning.
It's not gory at all, there's not a single drop of blood. It's all the psychological end of things.
I wish they would have ended the movie a moment sooner -- I like open-ended things better. The ending as-is wasn't at all bad, it just could have been even better.
If you don't like dark movies, this is a big pass for you. But if you're interested in seeing how people act when in horrible situations, then The Circle might be a good fit for you.