The Assassin's Touch is the tenth book in the Sano Ichiro series. At the end of The Perfumed Sleeve, a power struggle led Japan to the brink of civil war and sent Sano's predecessor and nemesis, Chamberlain Yanigasawa, into exile. Although he eliminated his main competitor, Lord Matsudaira did not have a large enough faction to become Chamberlain himself so Sano, who allied himself with neither side, became Chamberlain.
Like most mysteries, The Assassin's Touch starts with a death. The head of the intelligence service dies during a horse race, and he is not the only official to have recently died in suspicious circumstances. The victims have all died suddenly, with no obvious marks or signs of violence. The Shogun orders Sano to investigate, and both the Yanigasawa and Matsudaira factions see Sano's potential failure as a way to replace him. Complicating matters, Sano's wife, Lady Reiko, has undertaken an investigation of her own.
Lady Reiko is an anachronism - an independent noblewoman and skilled martial artist who has helped Sano solve prior cases - and Rowland admits this by always explaining how unusual she is. Reiko is Magistrate Ueda's only daughter and he asks the daughter he educated like a son to investigate whether or not an outcast woman accused of murder actually committed the crimes to which she confessed.
The Assassin's Touch blends two types of mysteries - the "whodunnit" and the "whydunnit" - and they collide in the final third of the book. I admit that I wasn't surprised by the solution to either mystery or the connection between the two, but it took enough effort to solve them that I didn't feel cheated. Like the rest of the Sano Ichiro novels, The Assassin's Touch includes a climactic battle scene, this time with a fairly small contingent of samurai and including a one-on-one battle between Sano and a samurai reputed to know an obscure martial art.