A young woman, Jade Yamata, is struck with a blade that was flung at her chest from the darkness of an alley. The victim was a Japanese citizen who had been in the country for six months. Castle theorizes she was killed by a circus knife thrower. The Great Throwdini, perhaps? A drop key, like the ones used in old buildings to manually open elevator doors, is found at the scene.
Jade's boyfriend, Dean Bedford, says Jade was a student at a ballet company. His parents are patrons of the place. As for the drop key, it's linked to an abandoned building that was home to a cookie factory. It's not far from where the victim was found. The key leads to a section of the building that has a small shrine. Castle finds a blade that may be the murder weapon. A noise is heard. It's a ninja, who promptly steals the murder weapon and disappears in a cloud of smoke. It's all such a cliché, right?
A representative of the Japanese consulate says the symbols found in the shrine don't suggest the killer is a ninja. Those warriors simply don't exist anymore. Castle doesn't want to accept this even though evidence suggests the killer could be a ballet dancer named Lee, who had a heated exchange with Jade. Hey, he could be a ninja, too. Well, not really. Lee drops a mug Castle tosses at him. A real ninja would have caught it. Lee says Jade was going to quit the ballet company.
While Beckett keeps a dinner date with an annoying old friend, the boys check out the tea import company Jade was calling nightly. It's a front for a Japanese hostess bar. Castle, Ryan and Esposito mingle with some of the ladies. It's the only way they can get info. Castle retires to a backroom with one of Jade's friends. They are all over each other, but only so they don't raise suspicion. Castle learns that Jade got invited to a private party being held by a patron named Saito. Everyone fears this guy.
One of the working girls lets her boss know that Esposito is a cop. This occurs while Ryan is up on stage belting out "What I Like About You" karaoke-style. The boys are escorted out of the club. Castle is also tossed, but not before getting a $6,000 bill. At least he learned Jade was in trouble because she was going through Saito's things. That's the good news. The bad news is Castle has lipstick on his collar and forgot make a bailout call to Beckett to save her from her annoying friend. The hits just keep on coming when a ninja appears in the alley.
The ninja attacks all three boys and quickly gets the upper hand. It doesn't look good until another ninja shows up to help. The first ninja warns the cops to stay away before making a stealthy escape. The second ninja also tiptoes away in the blink of an eye. Later, Castle briefs Beckett on what went down. She's understandably miffed about his shenanigans with the hostess, but she's also upset that her friend was so boring last night. All she did was complain about her husband. Beckett worries that marriage may make them bored with each other. Castle assures her that won't happen. They can even add a promise to their vows.
The team learns that Mr. Saito is a big name in organized crime. The man has throwing stars in his office like the ones that were used in the alley attack. In other news, the woman who showed up as a consulate officer is an imposter. She was trying to throw off the investigation. In fact, Jade may not even be the victim's real name. An autopsy suggests she was treated by a U.S. military surgeon as a kid in Okinawa.
A family was murdered after the dad, a building contractor, had a disagreement with the local gang which has ties to Saito. The family was killed by an enforcer known as the Green Dragon. The youngest daughter escaped the carnage. It was Jade. She was looking for proof that Saito is the Green Dragon.
When word gets out that the ninja has returned to the lair, Beckett is there for the arrest. She finds the woman who impersonated the consulate officer. She's a cop. She's also Jade's sister. She also survived the family murder. She says Jade tracked down a businessman who could lead her to the Green Dragon. It happens to be Randall Bedford, dad to Jade's boyfriend, Dean. The guy was in business with Saito.
Dean is furious that his dad didn't do anything to stop Jade from being murdered. Randall claims he was just trying to protect the family. Beckett gets a warrant to arrest Saito, who is shot dead when she and Castle arrive. A ninja holds a gun out. He's the real Green Dragon. A second ninja springs out to take the first one down. Ninja Number 1 is unmasked. It's Randall Bedford. Ninja Number 2 is Jade's sister. The strange case is closed and a sure indication that life with Castle and Beckett, be they married or not, will never be boring.