The film takes place in the early 1940s, in the British colony of Kenya. The focus is on a community of privileged and decadent British aristocrats, who live in the area known as Happy Valley. Sir Henry "Jock" Delves Broughton, 11th Baronet, a businessman in his late fifties who has invested in a large farm in the region, joins his fellow British settlers, accompanied by his stunningly beautiful young wife, Diana (played by Greta Scacchi). The story develops from there.
It is a captivating and interesting film, which succeeds in reconstituting extremely well the toxic and claustrophobic colonial atmosphere prevailing at the time in East Africa: it is Kenya during WWII but it could be anywhere in British-ruled Africa c.1880. The tensions and dramas that characterize the movie are purely internal to the European community: the Africans are relegated to the role of servants, chauffeurs, and so on - an accurate depiction of conditions at the time.
Greta Scacchi was at the height of her amazing beauty when the film was made and her acting is also excellent: she is at the centre of the film and carries the whole story through. Diana - the character she plays - comes from outside and her presence in Happy Valley triggers what can only be described as an emotional, psychological, sexual and social earthquake in the close-knit British community. So, the story is, ultimately, about her and the impact she has on people around her - more particularly on the white men who have fallen for her.
This is a very good film, almost melodramatic in some respects, and yet, it is based on a completely true story which you can read about on Wikipedia after watching the movie. (The film is generally faithful to the historical events as they are known, so, you should not read about them before watching the film.)