WARNING: I assume you mean you want the entire plot. If you don't want to know who dunnit yet (if you haven't already finished watching) don't read on.
Lots of stuff happens. To get us started, Mrs Wilson poisons William, Robert Parkes stabs him. Robert is William's bastard son, and wants to kill him from hatred. He doesn't know that Mrs Wilson is his mother, as he thinks his mother is dead. Mrs Wilson anticipates this and kills William herself, so that the police can never touch her son.
Mrs Croft is Mrs Wilson's sister; the enmity between these two stems from when Mrs Wilson gave up her kid for adoption (William actually just takes the kid to an orphanage) to keep her job. Mrs Croft also once got pregnant to William ('randy old sod') and lost her job to keep her child. The kid died anyway, so Mrs Wilson made Sir William take Mrs Croft back as a worker.
Anthony Meredith (m. to Lavinia, who is Sylvia and Louisa's sister) runs some sort of business which William is invested in or something. William is soon planning to pull out his funds, thus ruining Anthony. He is accused of trying to shoot William.
Sylvia, Louisa and Lavinia are sisters from a poor aristocratic family. Louisa and Sylvia cut cards to marry William, though Louisa and William actually like each other. Louisa marries Lord Stockbridge, whom Robert decides to work for to get to William.
Freddie Nesbitt is married to Mabel. She was the daughter of a factory owner or something; he married her for the money he thought her father had. It wasn't as much as he thought, so now he's poor with a wife he doesn't care for. There is/was something going on between Freddie and William's daughter Isobel. Freddie is trying to make Isobel convince her father to give Freddie a job, and he's using whatever happened between them to blackmail her.
Rupert is chasing Isobel cos he thinks she'll be rich when her daddy carks it. His friend Jeremy is the dark-haired one fooling around with the kitchen maid, Bertha.
Ivor Novello is William's cousin or something. He's an actor. His friend Morris Weissman, American director of the Charlie Chan films, has joined the shooting party for 'research' for his next film, 'Charlie Chan in London'. Weissman's 'manservant', Henry Denton, is acutally an actor also researching for the film. He tries to get a shag wherever he can, and Lady Sylvia is forthcoming.
Elsie, head maid, is having it off with William. She reveals herself accidentally on the night of the murder, so she'll lose her job. (As to her end, I reckon she'll become an actress in Weissman's film: he's looking for British girls, she has an interest in acting, and she looks the part).
Mary is the main character, so I s'pose I should've mentioned her first. She's newly hired by Lady Trentham (old windbag who lives off her allowance paid by William, who may shortly cut it off - until he dies). Mary uncovers the murder. Robert fancies her. She's pretty cute, and she turns out to be a loyal servant for Trentham.
The bumbling detective is messing up the case (note that he touches pretty much everything that has fingerprints: whiskey lid, whiskey glass, etc.). He is dumb, and his constable has more of a chance of solving the case, though probably won't as the links are too far apart to be made.
I can't really think of anyone else at the mo'.
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