Jim Brodie is an antique dealer in San Fransisco who als inherited his dad's security firm based in Japan. He also consults for the local cops on matters Asian and antique.
When an entire family is slaughtered in the San Fran neigborhood called Japantown the cops ask him to show up because there's a mysterious Japanese character painted there. Brodie is more than interested because the last time he saw that character it was at the scene of his wife's death.
As he investigates he travels to New York and to Japan where he joins the guys from his dad's firm to find out who is behind the murders. What he encounters is an ancient and very dangerous group of assassins that endanger not only his life but that of his daughter as well.
There's a lot of mysterious ancient Japanese secrets and societies, martials arts and conspiracy stuff. Basically, the scale is a bit bigger and international than I usually like, but Brodie is a capable leading man and the story very well researched.
Read it if you're a fan of the authors mentioned at the beginning.