A westerner named Casey Bowman has finally settled into a quiet life in Japan, mastering the skills of the Koga ninja under the tutelage of his sensei, Takeda, and marrying Namiko, Takeda's daughter. He runs a dojo and lives a simple, content life with Namiko, who is pregnant with their first child. However, his world is shattered when he returns home one night to find Namiko brutally murdered. With his life torn apart, Casey is consumed with the need to avenge his wife's death. He begins to suspect that a drug-trafficked gang with connections to his past might be responsible.

The path of vengeance leads Casey to ask for help from his friend Nakabara, who invites him to his dojo in Thailand. There, Casey refines his martial arts skills and embarks on a relentless quest to track down the attackers. His journey takes him into the seedy underbelly of the Asian underworld, where violence and betrayal wait at every turn. He mistrusts everyone, confronts a host of lethal adversaries, and navigates through the dangerous terrain while piecing together clues that draw him closer to the truth behind Namiko's death. As darkness envelops him, Casey finds his ninja training put to the ultimate test in both physical combat and mental resolve, while he seeks retribution without succumbing to the shadows of despair and rage.