Crown of Lies and Silver. The Hollow Crown Series, #3

She came to the palace to gather intelligence. She leaves it holding something far harder to file. Seraphina Voss is a Threadwitch - she reads the emotional bonds between people with the precision of someone who cannot turn the ability off. For nine months she has used that skill in service of a mission she believed she understood. She was wrong. The evidence is sealed. The leverage was a lie. The man she was sent to ruin is safe, unaware, and sending cheerful letters.
And the Crown Prince whose grief she can read across forty feet of ceremony hall is formally promised to someone else. Seraphina is learning to hold things she cannot fix. She is not good at it yet. Then a letter arrives with one line, no signature, and perfect timing. The conspiracy she spent nine months inside was not the whole conspiracy. It was the part someone needed her to see. The part she was never supposed to find is in an archive she has had access to all along.
The Hollow Crown Series, Book Three.