The Japanese Corpse

Description for THE JAPANESE CORPSE by Janwillem van de Wetering:

When the beautiful Japanese woman appeared in the grubby offices of Amsterdam's Murder Brigade, Grijpstra and de Gier were stunned to hear her story: she and the boyfriend she reported missing were part of the notorious Japanese crime syndicate, the yakusa. Both Holland and Japan wanted to stop the flow of stolen art and drugs from East to West, and the commissaris and de Gier were dispatched to Japan. Working undercover, they soon became pawns in an international game that would settle the score between the yakusa and Europe, once and for all.

This is #5 in A Grijpstra and de Gier Mystery.