Inevitably, Lee gets curious and breaks the law to get hold of some books to try to understand what people are believing and doing. She's quite shocked to discover that this highly irrational crap has been going on for a long time, for all that it has only recently become the fashion. A group of merchants (including a guy who owns a string of bordellos) is attempting to recruit Taro and Lee for who knows what, and Lee is sick and getting sicker.
Oh, and Taro keeps shielding events happening somewhere else a long ways away and it's really messing with Lee. Then the Empress dies and they get invited (ordered) to attend the coronation, where the heir proves to be Even Worse than expected.
Huge cliffhanger at the end here, so, (a) don't start with this entry in the series and, (b) consider waiting until the next book is out before starting this one.