Jade Yamata is killed by a mysterious attacker who threw a knife in her chest. When Castle and Beckett later find what looks like the murder weapon, a ninja appears to steal it back.
Castle, Esposito and Ryan go undercover at a geisha-like hostess bar where Jade worked. Turns out she was tracking the Green Dragon, the man who murdered her family back in Japan when she was a child. Only she and her sister survived.
Jade believed the Dragon was Mr. Saito and dated to son of someone who did business with him. Turns out the Green Dragon was actually her boyfriend's father, who killed her to keep his secret.
After meeting with an old friend for dinner, Kate is worried that she and Rick will become boring after they're married. Castle promises to write a promise to keep the romance alive into their vows.