Castle is psyched to hit a screening of Forbidden Planet. He knows Alexis is fibbing about her reason for not wanting to be his movie date. Castle's curiosity as to why she lied is put on hold after a juror in the high-profile murder case of socialite Lila Addison drops dead during closing arguments. Lanie says the guy was poisoned. Now Castle and Beckett want to know why.
Joe McUsic was Juror #7 in the case against Otis Williams, who benefits from a mistrial. McUsic's brother, Eddie, says Joe always looked out for others. Another juror says he was intimidated by Wardell Williams, the cousin of the accused. Surveillance video shows Wardell handing the victim a cup of coffee inside the courthouse that may have been laced with cyanide. Castle says, "Looks like he makes a killer cup of joe."
Wardell claims his cousin is being framed as part of a conspiracy. Why else would District Attorney Lou Karnacki (guest star Bruce Davison) be trying the case? Turns out Wardell didn't poison Joe's coffee. The juror died from cyanide that was in a time-release capsule taken before he even got to the courthouse. The detectives discover that Joe actually bought his way onto the jury for the Otis Williams case.
Lila Addison's brother, Stephen, assures the team that his sister didn't know McUsic. Even if she did know Joe, he wonders why this guy would put his sister's shot at justice in jeopardy. D.A. Karnacki wants old friend Roy Montgomery to keep him in the loop regarding the investigation. Surveillance photos show Joe McUsic was at Lila Addison's crime scene. Castle deduces, "He's our victim and our killer."
Joe had an alibi for the time Lila was killed. So why was he at the crime scene? And why did he want on that jury? Ryan discovers that Joe made a bunch of calls to D.A. Karnacki. He claimed that he was mailing evidence that would exonerate Otis Williams. Captain Montgomery now believes his friend may be hiding something.
Castle and Beckett are open to the conspiracy theory. Lila Addison's folks were big contributors during Lou Karnacki's last election. Otis Williams claims he pulled up the seat in the car where the murder victim was found dead in the trunk. Someone other than Lila was driving that vehicle. Prints on the seat controls are a match for Joe McUsic's brother, Eddie.
Eddie McUsic knew the victim. He also knows her brother, Stephen. The rich siblings were a couple of spoiled coke fiends who used Eddie to make a drug run. Stephen was holding a gun when the car hit a pothole. BANG! The gun went off and killed his sister. Eddie knew Stephen had the power to frame him if he didn't help with the cover-up.
Eddie told his brother what happened. Joe then tried to save the innocent Otis Williams by becoming a juror. He also sent a package containing Stephen's bloody clothes to the District Attorney. Captain Montgomery pays a late night visit to Karnacki's office. The D.A. promises to make his old pal Roy the next Police Commissioner if he just lets this thing go. That's not going to happen. Case closed.
In other news, Castle has a super-cool app that allows him to track his daughter's cell phone. As you can imagine, Alexis gets upset when she realizes Big Father is watching. She then tells Castle that some of her friends shoplifted stuff from a boutique. Alexis returned to the scene of the crime to pay for all the items. She refuses to name her shoplifting friends, which makes Castle both angry and proud.
Later, Castle is jazzed that he'll finally be able to catch that screening of Forbidden Planet. It won't be with Alexis though. No, Castle plays dumb about the classic sci-fi flick in order to elicit a movie date from Beckett. Well played, Mr. Castle. Well played.