Massacre at Shirakawa — I.J. Parker

On the eve of the Tanabata Festival, a warrior rides into a family gathering to slaughter the members of a high-ranking family and their guests. Akitada, whose best friend is among the victims, searches for a shadowy killer who may be part of a secret conspiracy against the emperor himself. In his determination, he defies orders, involves his friends and his sister, and puts his family in danger. Meanwhile, his faithful retainer Tora risks life and limb in a world of thugs and prostitutes to solve the bloody murder of a schoolmaster's wife. Both will suffer the consequences of pursuing ruthless adversaries who are determined to ruin or kill them.