Warrior Spirit (Rogue Angel, Book 9)

the long version

A priceless artifact could restore a family's honor--or destroy everything in its wake.While vacationing in Tokyo, archaeologist Annja Creed is approached by a man who desperately needs her help. Kennichi Ogawa, the last descendant of an ancient warrior family, is trying to locate a stolen artifact. Legend has it that the vajra was mystically endowed by a warrior's spirit to help the Yumegakure-ryu family forever be a source for good. But the vajra could help the forces of evil if it gets into the wrong hands. And now the bloodthirsty Yakuza and a group of hired ninja are after it. As Annja and Kennichi trek through the fog-enshrouded mountains of the Iga province to find the relic, they must also outsmart the vicious Yakuza and ninja who are dangerously close to uncovering the vajra first...and to destroying their competition.