I have read a book in the 90's, while I was a teen, but it is very likely it was published much earlier. I have been trying to find it on and off since. I do not remember character names. Sorry. Things I do remember:
- The book is of novel length
- Technology level is middle 20th century. No magic. No personal computers.
- Point of view character is a man.
- The book starts with the man going to huge property (with a house) of a millionaire, who is his friend. Millionaire became millionaire by revolutionising steel industry, I think.
- It is possible that they are friends from after the war. I think WWII but I might be wrong.
- While a driver or his friend is driving him to the house, the man sees a tractor ploughing the field. The tractor has no driver; it is tied with steel cable to a steel or iron boulder and is going by itself in ever shortening circle as the cable winds up. The millionaire explains that the tractor is one of his automation experiments; he wants to revolutionise agriculture the same way he did steel industry. That means circular field which can be worked on with automated tractors, with houses and storage on the edges of formerly square fields. That's the only sci fi part of the novel.
- The millionaire has a beautiful wife. She loves him very much, but is something of a wild spirit, a force of nature. She likes to ride horses, she likes speed, is a good swimmer etc. Sort of like Teddy Roosevelt in female form, if that makes sense.
- I remember a scene near the start of the novel. The man is introduced to wife, there is a pool party after a while and millionaire friend tells him that she can hold her breath for 20 minutes or something like that. There is a bet involved, I think. The wife dives in and does not dive out. The man sees that nobody at the party is worried so he realises it's a trick of sort. He dives in too, multiple times and she is nowhere to be found in the pool. So he dives in one last time and finds a hatch to secret underwater chamber where there is breathable air and she is inside. It might not have been pool, maybe some small (artificial) lake on the property.
- They fall in love, the man and millionaire's wife. I am not certain if they ever slept together, but they were deeply in love. The man feels bad about messing with his friend's wife but the millionaire is not that much conflicted although it is very tricky situation. They are two people he loves most in the whole world, one as his best friend and one as his wife and lover. He is intelligent man, a genius if you will; he doesn't want to ruin friendship and marriage just because his best friend and his wife love each other. I think that he even jokes at one point, something like: "I was worried you two won't get along. I shouldn't have worried, I guess." . Yet, it is a conflict that needs to be resolved.
- Near the end of the book, some sort of accident happens. Either horse bucks and the wife falls or something like that. Anyway, the result is that her neck is broken and she is unconscious. I am not certain whether she wakes up to have a last talk with her husband and his friend. What I am certain of, is
- The family physician/ property doctor checks on her. Even if she wakes up or survives whatever happened to her, she will never walk again. The heartbreaking decision is made: the doctor will inject her with lethal dose of morphine and she will perish without pain, instead of suffering the rest of her life as para/quadriplegic, which would be worse than death for a free spirit like her. I am not certain whether she was awake to help them make that decision, but they do just that. I do not know whether it is doctor doing the injecting or her husband or her lover but she dies at the end of book.
- I think that one of character names might be Henry.
Edit: Language is English and it is all happening in US.
That's all I remember. Any help is appreciated.