The Ronin's Mistress is the fifteenth book by Laura Joh Rowland in the Sano Ichirō mysteries series. It was published on September 1st, 2011. It was preceded by The Cloud Pavilion and followed up with The Incense Game.
"In the fifteenth book in her brilliant series of samurai thrillers, Laura Joh Rowland presents a fresh new take on the legend of the 47 ronin, one of the most famous true stories in Japanese history.The year is 1703. On a cold, snowy night, 47 samurai attack the man they blame for their master's death and cut off his head. The vendetta is the ultimate act of loyalty that a samurai can perform. But it creates a firestorm of controversy, unanswered questions, and a serious dilemma. Why did the men wait so long to avenge their master's death? What should be done with the 47 ronin, who have fulfilled their duty to their master but broken the law? Should they be praised as heroes or executed as murderers?
Sano Ichiro, who had once been a ronin himself but had risen to the rank of Chamberlain, has been demoted to his former post as the shogun's chief investigator. The shogun orders Sano to find a seemingly impossible way through the maze of conflicting stories and loyalties. When Sano and his wife Lady Reiko investigate the case, they discover that the truth about the vendetta may hinge on the ronin leader's beautiful young mistress. The solution to the mystery goes straight to the heart of Bushido--the Way of the Warrior, the samurai code of honor." 
- Yanagisawa Yoritomo