Sorry to resurrect this old thread, but I’ve just finished bingeing this over the past couple of days and need to discuss!
I think the unreliable narrator has been done really cleverly, and the level of ambiguity just right - after all, in real life not everything ties up neatly with a clear explanation. I think piecing together the fragments and possibilities give a tangible explanation. I do wonder what Christina’s evidence would have been! But again, that probably would have brought too much out into the light.
Regarding points made above, I think that Harriet was definitely the anonymous benefactor who bought the painting, I thought so when it was first mentioned. So her trip to Glasgow was planned with meeting him in mind, she developed an obsession as shown at the end when we see she has his missing stud.
I doubt think there’s meant to be any doubt that the events happened, that’s not what I took from it. I was totally fooled by the Sarah/Sybil thing, it’s only the later dealings with the agency that shows how many companions she’s gone through and that she’s clearly deteriorating with age and illness, and unable to charm/control people as she used to. Also the allusions to the drink problem. I thought the flies etc were due to her not cleaning and rotting food (and rotting bird!), but who knows, maybe Sarah didn’t leave the flat! I don’t think she’d be that crude though.
Even though she’s clearly a troubled, awful person, I did have some slight sympathy for her. The rejection and abuse from her stepfather was awful and must have triggered her desire for a lover/father figure. I did wonder if there was a hint that she may have put her mother out of the way - she died from ‘botulism’ from asparagus they had bottled - a first iteration of her poisoning tendencies? Her mother was a competitor for her father’s attention. Or had they split up by then? Anyway, thought it could be a suggestion.
Sorry for the brain dump! I think this ones going to stay with me for a while…