The Way of the Ninja

A Japanese woman named Jade is killed while looking for those responsible for her parents' deaths when she was young. Castle finds the murder weapon, but it is taken out of his hand by a ninja. The investigation leads them to a Mr. Saito, who is affiliated with the yakuza. He is killed and Castle and Beckett would also have been killed, but they are saved by Jade's sister, Saya, the ninja. The killer was an American contractor for the yakuza.