
Spoiler:
So basically, Karel was captured when he was in the field. The reason why his friend thought he was dead because they wanted Karel to assume another identity thus, “Skar”. They offered Karel either his life or him to turn into a spy. Because he wanted to go back to Sasya, he chose being a spy. Him treating Sasya horribly was basically him testing Sasya because obv he was mad at Sasya “leaving” him. Sasya didnt reqlly leave him but left the house specifically. Sasya wrote this in the letter and explaining other things that unfortunately was never delivered to Karel. So Skar will marry the duchess (only a contract marriage) but Sasya will mentally suffer because of this and turning to opium for comfort. It got so bad that he visibily intoxicated in the streets and Skar had to make a scene where he was cutting off Sasya because he was to clingy just to hide from other people that Sasya was high in opium. And then Sasya gets captured on the suspicion of being a spy. He gets lockedup and hears that Skar is also under suspicion. If I remember right, at this point he now knows that he was the one the killed that soldier and Karel took the fall for him (?) so he decides to protect Skar and confirm to the guards that yes, he is the spy so they’ll stop being suspicious of Skar. Because of this, he’ll get the death penalty. He is happy with this because for once, he’ll be protecting Karel, and not the other way around. At this point as well, Skar has also discovered that Sasya “leaving” him was a huge misundertanding as he has already received the unsent letter Sasya sent him before (the one explaining that he’ll be in Paris etc) He rescues Sasya and they run away to America. Sasya dies in america after a few years (i think because of old age) and once Karel comes back from Sasya’s funeral he shoots himself and commits suicide as he has nothing to live for. But I believe they spend multiple happy years in America, it’s just that Karel refuses to live in this world without Sasya.
There’s a lot more details in the spoiler thread, just google.
I read the novel spoilers until the end and oh my god poor sasya