There is something oddly sad about Flavia's little speech when Rassendyll announces he's going boar hunting (just as a way to catch Michael) out. She had assumed they would be going riding together. The way she says "I'm sorry we're not able to amuse you enough here" is said stoically but you can tell how hurt she is. Thankfully Rassendyll lets her in on the plan immediately.
To say nothing of the final goodbye between him and Flavia. He begs her to come with him, but she says she can't desert her duties to her country — no matter how much it breaks her heart to do so.
Rudolf ends the book thinking about Flavia, and whether he'll ever see her again.
Shall I see her face again—the pale face and the glorious hair? [...] I do not know. In this world, perhaps—nay, it is likely—never. And can it be that somewhere [...] she and I will be together again, with nothing to come between us, nothing to forbid our love? That I know not, nor wiser heads than mine. But if it be never— [...] why, then, this side the grave, I will live as becomes the man whom she loves; and, for the other side, I must pray a dreamless sleep.
Rupert of Hentzau
The death of King Rudolf. A mix-up with messages leads to the King going to the hunting lodge shortly before Rupert arrives, and his friends don't get there in time to save him.
Even though he's the villain, Rupert's death is pretty sad.
