Gosford Park (2001)

Boy, they certainly took their time getting to the murder. The murder doesn't occur until more than an hour into the film's two plus hour running time.
To no one's surprise, Julian Fellows (the genius behind Downton Abbey) wrote the screenplay and assembled an utterly brilliant cast with probably too many characters. But here, everyone matters, and everyone has an interesting back story, both the upstairs wealth and the downstairs servants. And the murderer is not who would expect, as there are technically two murderers. The rapist, Sir William (Michael Gambon) is both poisoned and then, stabbed. And the detective (Stephen Fry) can't seem to figure out what actually happened and there are plenty of suspects and twists along the way.
Turns out William used to own factories before the first world war (this film occurs in fall of 1932) and constantly raped his employees, impregnating several of them, including both his current housekeeper, the stiff and radiant Mrs. Wilson (Helen Mirren) and snarly cook, Mrs. Croft (Eileen Atkins, who has some great zingers). But he deposited the babies at an orphanage instead of arranging for them to be adopted as he promised and that is not something Mrs. Wilson can abide.
Now, while I wouldn't have predicted that Sir William, who loves his dog more than his wife, was such a wretched human being, I did feel that one of the guest's valet (Clive Owen) for a guest was indeed Mrs. Wilson's son.
There are a few side plots that are just odd, including Ryan Phillippe's Henry, pretending to be Scottish, disguised as a valet, when he is really an actor and potentially the lover of Hollywood director Weissman (Bob Balaban), despite nearly raping a maid and sleeping with the dead man's wife (Kristin Scott Thomas). Still, despite everything, this is an excellent film with superb acting who turn a trifle into something special. While the murder took forever to come by, and everything is wrapped up too quickly, I could have continued watching this film with this cast of actors and characters for hours more. Grade: B+
Side Notes:
-Maggie Smith also shines as Her Ladyship, who adores gossip about everyone else and their servants. Kelly MacDonald is great as her young, inexperienced maid who falls in love with Clive Owen.
-Maggie Smith's servant in Downton Abbey, Jeremy Swift (Pratt) is also a servant here.
-A blond Emily Watson is another servant, and possibly the only one who actually liked Sir William, which is good considering that she was sleeping with him, but her adoration also leads to her downfall.
-Those Brits love their dogs.
-They don't understand how anyone can be a vegetarian.
-You should always make sure your knives are accounted for.