He wasn't. Tadatoshi had been murdered and his body buried near a temple. When the Shogun orders Sano to investigate, Matsudaira sees a way to push his rival aside, especially after he learns that Sano's mother may have been involved in the crime. If Sano does not solve the crime, he will at the very least be thrown from power, but if his mother is a murderer, then he and his wife, children, and retainers will all be executed as well. While solving the murder that may lead to his own death, Sano must also flush out his old enemy, Yanigasawa, who has escaped from exile and may be behind the current unrest. Rowland nicely ties questions of family, loyalty, and justice into the web of political intrigue, and even manages a happy ending for a few of her characters.
She's also dropped the mystical undertones of her past few books and that gives The Fire Kimono a more even tone than her previous few outings. Like most series, it's best to read the Sano Ichiro books in order, but this one is well contained enough to serve as an introduction to the series.