The episode begins at a busy restaurant, where the waiters collect the orders from the kitchen. It is seen that someone (face not shown) sprays something on one of the plates. This plate is served at one of the tables, where a group of four, is having dinner. All of a sudden, the older man, Arthur, dies right at the table. At home, Castle is busy playing video games with a guy named Patel, online. Kate tries to seduce him, but he is so engrossed that he ignores her. Kate is pissed.
Later, they arrive at the crime scene. Ryan briefs them about the victim, Arthur Felder. Arthur is a venture capitalist. He took one bite of his squab, and he “nose-dived into his plate”. Lanie tells the team that this is not an allergic reaction. Castle thinks that Arthur was poisoned. Castle notices Eric, the number one inventor and innovator. Ryan tells him that Eric Vaughn was dining with the victim. Kate and Castle talk to another man and a woman, who were dining with the victim. Eric is talking over the phone when Kate tries to question him. He ignores her and Kate gets pissed. He tells Kate that he was making arrangements for Arthur’s family to fly down.
Esposito arrives and tells them that the kitchen door was propped open and a waiter’s suit was found in the dumpster. Kate decides to question the kitchen staff. Castle finds Kate staring at Eric. At the precinct, Ryan is questioning a waiter, who tells him that he noticed a short guy with dark hair, in the back of the kitchen. He remembers that he did not look too familiar. Esposito arrives and tells Kate that Arthur shut down one of his plants, and 200 people lost their jobs. In the morgue, Lanie tells Kate and Castle that the poison that killed Arthur was not from any of his plants. She says that it is exotic, chemically synthesized and fast acting. She also says that it was some sort of a paralyzing agent.
She says that the mushrooms that Arthur ate did not even make it to his stomach. The topic then moves on to Eric, and Castle is jealous. Castle tells them that he read the menu, and he remembers that the mushrooms were served with the quail, not the sqab. They interrogate Luca, the waiter who served Eric and his group their dinner. Castle wants to know how Arthur ended up eating the quail. Lucas thinks that he mixed up the orders. He says that he is a new recruit and is still on the process of learning his job. Lucas looks at his writing pad and tells Kate that Eric had ordered the quail. Castle concludes that Eric was the target. Kate talks to Eric and tells him that the poison was meant for him. He is shocked. He tells her that he is unaware of any threats because his assistant would have told him, in case there were any.
Kate suggests that he should hire private security. Later, Gates arrives and tells Kate that Eric wants her to be his private security. Castle is pissed and jealous. Gates tells him that these are direct orders. Castle tells Ryan and Esposito that they need to solve the case as fast as possible, so that they can get Kate away from Eric. Esposito tells Castle that the cops picked up a homeless guy in the same alley where the uniform was dumped. Castle wants to interrogate this guy. At Eric’s office, Kate tries to convince him to let her investigate the case, rather than guard him. Eric thinks that she can do both. He then introduces her to his attorney, David Anderson. Lanie calls Kate and tells her that the poison used to kill Arthur is saxitoxin, which is normally found in shellfish, but not this version.
She tells Kate that this was synthesized in a highly sophisticated lab. Kate discusses this with Eric and his colleague. She learns about a talented researcher, Cindy, who had a fatal attraction for Eric. She also had access to saxitoxin. Ryan and Esposito interrogate Cindy. Cindy is shocked when she learns that someone tried to poison Eric. She tells them that she was at the opera at the time of the murder. Castle arrives and tells the duo that he’s got a lead. Castle tells them that the homeless guy identified the guy who dumped the uniform, Cory Harrison. Ryan is surprised because he spoke to Cory and Cory tried to pin it on somebody else. They go to Cory’s house and find him lying dead on his bed. The team arrives at Cory’s house and concludes that whoever killed Cory, is a pro, and that he might strike again.
They also find a bottle at the apartment, which contains saxitoxin. Gates tells Kate that she will have to go with Eric to the safe house, a Presidential suite, till the time the killer is found. Castle cannot take this anymore. Later, Ryan, Esposito and Castle go to the restaurant and talk to the Chef. The Chef tells them that on the night of the murder, Cory was late and the look in his eyes seemed like something bad had happened to him. At the precinct, Esposito tells Gates that Cory had a fixed routine. Castle shows Gates the security camera footage of the bus stop, where Cory usually took his bus from. On the day of the murder, they see a guy meeting Cory at the bus stop and handing him the bottle of poison.
They are unable to get a good look at the guy because his back is towards the camera. Castle theorizes that the same guy must have killed Cory, to tie up loose ends. At the precinct, a woman from the tech points out that the man who handed Cory the poison, is left handed. He also has a bandage on his neck, either to cover a wound or to hide a tattoo. Ryan arrives and tells Esposito that he showed the guys picture to Cory’s daughter’s pre-school teacher and she said that she saw this guy hanging around the school. Ryan thinks that the killer must have threatened Cory with his daughter and that is why he was terrified when he showed up at work.
Ryan and Esposito call Kate and tell her that the ballistics from the bullet that killed Cory shows that the gun was used for four other killings outside the state. They have a name; Thomas Barber. Eric doesn’t recognize the name. Later, Eric asks Kate if she and Castle are serious. She hesitates a bit and says yes. Eric tries to kiss her, but she lightly pushes him behind. At that moment, someone shoots through the window. The bullet misses the both of them. Kate pushes Eric to the floor. Later, the team arrives at the suite. Castle is surprised that the shooter knew where to find Eric because the suite was supposed to be a safe house. Kate describes the incident and something doesn’t add up.
Kate tells Castle that Eric missed being shot because he stumbled. Castle begins to suspect Eric. Kate tells him that Eric kissed her, she pushed him back and that is why he stumbled and missed being shot. Esposito arrives and tells them that the hotel across the street, positively identified Barber. It seems that Barber was staying at the hotel. Esposito also tells them that Barber made several calls to one number. Later, at the precinct, Kate and Castle interrogate Cindy. Cindy tells them that Barber told her that he was from a rival lab, and that they needed the patent first.
Cindy admits that she was mad at Eric and she also needed the money. She tells them that they only talked over the phone. She dropped off the vial at some place and the money got credited into an offshore account. It turns out that the money was transferred to the account by a company named Mexi solar, owned by Eric. They also find out that Eric had authorized the transfer. Esposito arrives and tells them that this company is a scam. Arthur had invested a lot of money in this company and was supposed to visit it. Castle tells the team that the only way to get away with murder is to make oneself look like the intended target.
He feels that Eric killed Arthur because Arthur was planning to visit a company that did not exist and this would bring out Eric’s lie. Eric is brought in for interrogation. Kate asks him about the company. Eric tells her that this is his company and he founded it. He says that he invested a lot of money in it. Kate tells him that this company has been shut down for a long time. Eric is shocked. He tells her that he has seen cash flows and other papers that prove that the company is doing well. He tells Kate that he did sign on the papers and the checks, but he does not oversee the day to day activities. Kate wants to know the name of the person who does.
Next, Kate and Castle interrogate Anderson, Eric’s attorney. They tell Anderson that the IT department traced the IP address which transferred the money into Cindy’s account, and it traced back to him. Anderson confesses. Case Closed. At the precinct, Eric thanks Kate. She tells him that they also caught Barber. At home, Castle has a surprise for Kate. He has lit the bedroom with candles and he tells her that he is going to give her a full body massage. Instead of being happy, Kate has a confused look on her face. The episode ends.