I've read the play on which this film is based. Possible spoilers.
Easy Virtue was an easy read, apart from the fact that my copy was second hand and had additional stage directions and acting notes, bits crossed out and the part of Charles highlighted by the previous owner! There was a rehearsal schedule and a photocall appointment too! It's all go in am/dram!
The play has a lot more characters than the Hitchcock film, and is very of its period, though Noel Coward himself said that things were changing and he was feeling very nostalgic when he wrote it.
In the play, the lead character, Larita, though beautiful, sophisticated and witty, is considered too old to be likely to provide an heir or other grandchildren, by the family, the first bone of contention, before they find out about her divorce, etc, a bit like the Duchess of Windsor. It is rather like that story, though it was written ten years earlier at least. The ending is very different though, John didn't have the makings of a king, or the strength to abdicate. Larita is a slightly flawed heroine, but a bit of a victim though she has become worldly and wise living abroad, and a sympathetic character.
A lot of very old-fashioned attitudes are displayed by three of the female characters, the mother and her two daughters. It is very much about the hypocrisy, self-righteousness and double standards of those days, and later, to a lesser extent.
It does have some very funny scenes and moments, but the ending is a little sad and there is just the slight hope of Larita later marrying an older and more worldly and likeable character, Charles Burleigh, and that Sarah Hurst may one day marry John Whittaker, despite her being very different to his mother and sisters, who had long been expecting John to marry her.
I would guess that Hitchcock put in extra scenes and had it arranged so that Larita was even more the star and to draw parallels between her manipulative and bullying first husband and her totally weak and unsupportive lover, and her organising and bossy mother-in-law and weak and passive second husband. This would change the character of the play a lot and lose all the humour and some of the insights, the subtleties of which would be difficult in a silent movie.
Larita's first husband was not in the original play, nor was her lover, and there was no trial, but they do refer to the husband divorcing her and the lover having committed suicide.
John's part is not all that big, or all that important. He is a weak but charming character and very young, not much more than twenty five, if that; his younger sister is just nineteen, and his older sister is not more than thirty; he is almost an anti-hero, he isn't really all that loyal and helpful to Larita, even before the chips are down. He is absent when the family discover her past. If they can't get RZ to play her, Kristin Scott Thomas could do it to a T. I have seen her play women like this, though in different circumstances.
Colonel Whittaker is a lovely, character, an old-fashioned gentleman, not at all pi and very warm. He seems to have been unfaithful, at least sexually, to his cold wife in the past and she is a very nervous person who complains about everything and everyone, thinking herself perfect. She seems genuinely upset by John's marriage and nearly hysterical when Larita's past is discovered by the younger daughter.
She is not being nasty to get attention or make capital, she has really poor, cold values and can't understand anyone who is not as cold and repressed, and repressive as she is. She is not the type to make a scene, really. Just coldly judgemental.
If I were casting this I would have Bill Nighy play Charles Burleigh and end up with Larita. They have mutual friends, and both seem popular in their own set.
Kristin Scott Thomas is much too beautiful to be the mother or the unfeminine older sister, (as is Julie Christie, though she would have made a lovely Larita a few years back!) Maggie Smith would bring out the mother's nervous twitches, low spirits and high dudgeon wonderfully well. I wonder if these two were once approached, and then the focus changed.
It would film well, as long as you took it off the stage and out of the drawing room. I would start by cutting between the family and friends in England; Father reading The Times, Mother giving orders to the gardener, the sister watching the other four characters playing tennis, from the verandah, the family dining at home with friends; and John and Larita in the South of France; meeting, Larita's French maid helping her dress for the first date, dining out alone, marrying, the pyjama clad couple having a pillow fight ending in a clinch; over the opening credits.
Then have scenes of him bringing the two together and just hoping it happens, and them first trying to get on and then slowly becoming more openly critical and hostile to each other and then the flaming row when the past comes out. This is one of two set pieces or highlights and the mother seems to get the upper hand and be in charge.
I would change the discussion of the Chinese Lanterns and fairy lights in the garden, which is just light relief, pun intended, to discussion of fireworks or a fear of threatening storms ruining the buffet or flowers to signal what is coming, wittily and pithily, especially as Sarah and Charles both already know about Larita. This discussion is re-echoed briefly before the second big scene towards the end of the third act, the ballroom scene, very funny, where Larita has her swan song, with Mrs Whittaker seeming bested, but actually very serious, with the mother about to get her way and John still vacillating. The actual ending is very wistful and sad and would work on film, but I would like a stronger promise of Charles meeting up with Larita later on, and John back with Sarah, even though she clearly as doubts and would need to lay some ground rules, like not living with her mother in law. Larita has made her promise to look after John, at least. Even in fiction, I wouldn't break eggs without making an omelette!
"I hate quotations, tell me what you know." Ralph Waldo Emerson.