Superficially, the story is simple: a dinner-party among 4 couples of friends, that just happens to be on a night that a comet is blazing closer to Earth. Someone mentions a curious set of events during an earlier comet passage, about a century before, and how that affected a local population.
Early on you can spot some slight "incoherences" coming from how characters exchange dialogues, and from the middle on, you start feeling spooked, as you start putting things together.
Be prepared for a movie that you will have to have the pleasure of re-watching 2-3x, in order to grasp every single detail and meaning contained in this mind-boggling experience.
What is more rewarding in all this rich and masterful script/ plot, is that it speaks so loud and clearly about how we lead our own particular lives and how we get where we are (or not...?). One way or another, you will look back on your own important decision moments in life and start wondering "what if...". A definite must. 9/10