What is this movie about?

I've seen the numerous trailers for this movie on HBO, but I still have no idea what this movie is about. Who is "Longford", he seems to be someone important enough to deserve his own movie, but it still doesn't tell me what the movie is about. I looked at the summary of the movie on this web pasge, but that told me even less. So I'm asking for an actual summary of just what this movie is. Help!