Murder in Black Letter — Poul Anderson

Meet Trygve Yamamura -- judo expert, Samurai sword connoisseur, and private detective. He is a triple threat to San Francisco crime. These combined skills enable him to keep his own head attached while finding out who removed someone else's with an honorable Japaneses weapon. An old-fashioned detective story, a genuine whodunit, with a good deal of suspense thrown in.