The Golden Kill(Black Samurai‪)‬

Alone and outgunned, Sand has two weeks to stop the largest gold heist in history
The Chinese diplomat walks into the revolving door just a step ahead of the grenade. Samurai Robert Sand is too late to save him from the blast, but as the smoke clears he is hot on the grenade-tosser's heels. In Central Park, Sand disarms the killer and knocks him unconscious. His name is Ivan Vanich, and he is posing as a Soviet operative. His real employer is a power-mad millionaire, who arranged the hit as part of a plot to upend a Russo-Chinese trading contract and seize the profits for himself. The diplomat in the revolving door was only the first to die.
On special orders from an ex-president, Sand races to avert catastrophe. His hunt for answers takes him to a sprawling English castle, where the samurai comes face to face with the man who would let millions die for the sake of gold.