It's been a few years since I read The Cloud Pavillion, so it seems appropriate that Laura Joh Rowland included a bit of a time skip between the two books. Sano Ichiro has spent the two years since we last saw him demoted to his prior position as the Emperor's investigator and remaining on guard against Chamberlain Yanigasawa's attacks. He feels his downfall is inevitable though, because Yanigasawa's son Yoritomo (the Emperor's current favorite) has changed from unwilling to enthusiastic partner in his father's plots. To protect the family, Reiko has begun to search for a wife for their 12-year-old son, Masahiro, but Sano's precarious political position has made most families wary of forming an alliance with the Ichiro family.
Then fate hands Sano a case that can save him - or send him into exile and leave his wife and children dishonored. The Emperor orders him to investigate the case of the 47 Ronin, 47 men who cold-bloodedly murdered the man they claim caused their former master's dishonor and execution. As Sano interviews the Ronin and other witnesses, Rekio interviews the wife and mistress of the Ronin's leader. Every witness has a separate story, and none of them are completely accurate. The Ronin's Mistress is a satisfying mystery, with plenty of plot twists which lead to a well-crafted action scene. My only complaint is that (again), Sano's deputy Hirata's mystical powers form a less than compelling subplot, and one that I suspect will drive the next book in the series.