I am looking for a book I read about 10 years ago. It was an eBook, and I believe the cover picture was very purple.
The basic premise of the story was there was a man on trial in a rural town, for killing his fiancee by convincing her to take a black market drug with him. The drug was designed to cause a sexual frenzy that was only appeased by having sex with the one you love. He was in love with his fiancee, but she wasn't actually in love with him, so she died.
A special judge drops by during the case, who has powers granted by the gods (I think?), his eyes are purple, and he travels on a train with two or three other people who are his retainers and friends. He goes into a trance when hearing evidence (I think?), then pronounces judgement, because he is this special kind of judge, his word is law. He pronounces the man not guilty due to it actually being the woman who gave them both the drug, and not the man.
The man travels with them until they get to their destination, then gets hired somewhere as a guard (I think?). He slowly falls in love with the judge over the course of the book, and ends up saving the judge's life when he gets dosed with the sex drug, and finds out then that the judge loves him back.