Dame Beryl Bainbridge was one of the most successful novelists Britain produced in the twentieth century, but surprisingly few of her works made it to the screen, and then mostly as television adaptations. The best known film to be made from her source was An Awfully Big Adventure, showing a catty side to Hugh Grant, but some fifteen years before that was Sweet William, for which she penned the script. It wasn't a huge hit, and there was a sense you'd be better off reading the book to get the benefit of her prose, but it wasn't a disaster either, capturing the interactions around the Ann character where people basically use her, either as a shoulder to cry on or as a verbal punching bag to vent their frustrations, and she is powerless to prevent this.
As this woman, Jenny Agutter could have played it strictly as a doormat, but imbued the role with a particular personality in that Ann was aware she was being sent from pillar to post by everyone in her life, but was hanging on to a small sliver of control when she knew that without her to absorb the impact of other's misgivings there would be a hole in their lives that nobody else could fill. Which is why the William of the title is probably the worst person to introduce himself to her downtrodden existence, as he may charm her off her feet, but he is also using her, at first for sex and then as proof that he can push people around, this influence illustrating to himself if few others what power he has over women. Ann is happy to fulfil that role, and as the relationship progresses she finds herself dug in too deep to extricate herself ever again.
For this reason, this tone of a protagonist being suffocated by everyone else's choices but her own, there are those who took against Sweet William as a pointless watch since there was nothing they wished to relate to in its ninety minutes or so, and if they were Agutter fans they would appreciate the by now de rigueur nudity, but not like the situation her character had landed in, no matter how well the actress portrayed the part with all its mood swings and contradictions, leaving the impression of a genuine person rather than an author's construct that Ann could have been in less sure hands. It was true not all audiences would get along with the movie, but it was very well cast, even Waterston who you would not at first glance consider prime womaniser material: he didn't play him as a cad, more a charmer.
As an aside, this was interesting too for its trailer; in the voiceover comedy In a World... the point was made that women just are not employed to provide narration on movie trailers, but for Sweet William there was an exception (though there was also a man butting in occasionally); perhaps it was only Hollywood previews this unwritten rule applied to. Back at the plot, after winning Ann over with a television on which to watch him interviewed by Melvyn Bragg (as himself) on The South Bank Show, William insinuates himself into her day to day routine, phoning her up to string her along then appearing at her door to jump into bed for afternoons of unprotected sex. You can guess how that turns out, yet even after making her feel like the only woman in the world who is right for him, we note him sniffing around other females like Ann's best friend Pamela (Geraldine James, getting an "introducing" credit), and then more women in his life are brought in, leaving us with mixed feelings. William has broadened Ann's horizons, given her self-worth, but chained her to his unreliability in an awkward result.