Based on the 1945 play of the same name by J. B. Priestley, the movie is set in 1912 mostly in the home of the Birling family just after a dinner to celebrate an engagement. Inspector Poole (Alistair Sim) arrives with the news that a young woman has died of apparent suicide, and over the course of the movie its shown that everyone in the house had something to do with the young woman's deteriorating circumstances.
Wikipedia's entry on the play makes it very clear that this a political allegory: '... the play was "rediscovered" and hailed as a damning social criticism of capitalism and middle-class hypocrisy in the manner of the social realist dramas of Shaw and Ibsen.'
The movie has no action, only talk. As the movie leaves no room for interpretation, it doesn't lay out moral conundrums about what could have happened: there's nothing to think about it, you're told what to think. Which leaves this as a rote lecture rather than an opportunity to consider issues. It's too heavy-handed in its opinions about social responsibilities to be interesting. Ironically, I agree with its message - I just can't take it delivered like this.