Japan, May 1695. During a horse race at Edo Castle the shogun's chief intelligence officer drops dead as his horse gallops across the finish line - the fourth in a series of sudden deaths among high-ranking officials. Sano Ichiro, now the shogun's second-in-command, is asked to investigate. A single fingerprint and an unexpected connection to Sano's wife, Reiko, puts Sano on the trail of an underground movement to overthrow the regime, and in the path of an assassin with a deadly touch.