"Castle" Season 6 Episode 4, "Number One Fan," Recap: Emma Briggs (Alicia Lagano) is a homicide suspect who might have killed her boyfriend at her flat. She escapes through a fire-escape before the NYPD can question her. Emma goes to a dental clinic and takes in hostages.

Kate Beckett (Stana Katic) is no longer an FBI agent. She also did not get her old job back at the 12th precinct as Police Commissioner had put a freeze on hiring because of budget issues. Rick Castle (Nathan Fillion) does not mind her no working status, which makes Beckett question, does he want to be her "sugar daddy." The two engaged couple' bedroom is invaded by Pi, Castle's mom (Martha Sullivan) and Alexis (Molly Quinn).

Before their morning gets completely out of order, Castle gets a call from Captain Gates (Penny Johnson Jerald) and is asked to come over. He and Beckett reach the place that is near the dental clinic. Captain Gates briefs them that Emma, the homicide suspect, wants to talk to Castle, and Castle does not mind doing that as he excels at talking.

Emma does not trust the cops and wants to have a face to face talk with Castle. To make sure, she is talking to Castle, she asks him some questions related to his books. Castle strikes a deal with her. He tells Emma that they can have a one to one talk if she lets go the mother and her daughter. Beckett gets worried. Castle assures her that Emma is her fan and he knows his fans, they don't harm.

Castle puts on his Writer's vest. Beckett asks him to get in and get out and not to do anything stupid. The code word they decide on is cheese burger if there is any sign of trouble. Emma lets Castle inside the dental clinic and sets free the mother and her daughter. Emma tells Castle that she does not have any demand but she wants him to prove her innocence, and that she did not kill her boyfriend, Angelo. Emma thought that Angelo was going to propose to her on her birthday, which is that day. She tells Castle that she came back home later after buying a dress for herself and went to sleep after having a glass of scotch. In the morning, Emma woke-up to find Angelo dead in a pool of blood.

Beckett wants to know from Captain Gates if they had done a background check on Emma as she seems to have a deep-rooted distrust against cops. She gets the permission to go to the murder site. At Emma's flat, Esposito (Jon Huertas), Ryan (Seamus Dever) and Lanie (Tamala Jones) are already there. Lanie asks Beckett what she is doing there as she should be preparing for her wedding.

The evidence at Emma's place indicates that Emma is the murderer. She had told Castle that she had one glass of scotch, while the bottle at her place was completely empty. There were messages on Angelo's phone from Emma, which shows that she suspected him of having an affair. Emma had sent a message to Angelo, telling him that she was drunk, lonely and wanted to see him. Also, she was on medication for psychotic disorder and moodiness.

Beckett informs Castle about the new findings. Castle tells Emma that it is possible that she does not remember what she did in her drunken state. Emma insists that she is innocent but the new revelation makes her doubtful. Castle checks her text messages and asks her how she writes love you. Emma tells Castle she uses short-forms to do that. The last sent message from Emma's phone had spelled-out Love You. She puts the phone in a bag and tells Castle to find finger-prints of the person who used her phone as that person must have killed Angelo.

At the 12th precinct, Castle tells the group that Emma must be telling the truth and that she must have been framed. Captain Gates allows Castle and Beckett to work on the case and assigns them to the new detective Sully. Castle and Beckett do not find any motive behind Angelo's murder. He had a history of petty crimes but then he really had turned his life over for the better. Sully informs Castle and Beckett from the field that from Angelo's car, he found burglary tools and that he was keeping a watch on a house, three days ago.

Castle goes back to the clinic and questions Emma about Angelo's record. Castle gets a call from Beckett and she tells him to listen quietly, without reacting. Beckett informs him that Emma has been lying and that she has a jury record against her. She had killed her foster brother with a knife in the basement of her foster home. The same way Angelo died, too. Castle wants Emma to tell him everything. Emma asks him to believe her and that she did not kill Angelo. She did not have a good time at her foster home and the two brothers at the foster home used to bully her. Emma said that she had accidently killed one of the brothers to protect herself when they had tried to attack her in the basement. The brother who survived testified against her. Emma tells Castle that Sisters of Saint Helena's home for children had helped her.

Emma had wanted to find about her biological parents. Castle figures out that Angelo must have broken in to the home for children to find information about her biological parents. Before he could work on the new finding, one of the hostages try to snatch the gun from Emma's hands. Castle gets shot in the chest, accidently but his Writer's vest saves him. The NYPD and the hostage rescue team barge in and handcuff Emma.

Castle tells Beckett that he knows who killed Angelo and that it must be one of the biological parents. In addition to Emma's adoption file getting stolen, her sealed jury record was also opened. The opening of the jury record leads the NYPD team to a high-profile attorney. He refuses to answer any of the questions. Esposito and Ryan find Emma's adoption file from Emma's place, wrapped as a gift. The file reveals that the father is a powerful real-estate builder who intends to run for the Governor's post. He is called to the 12th precinct on the grounds of suspicion. However, the high-profile attorney turns out to be the murderer and is the son-in-law of the real-estate builder. The attorney feared that if Emma finds out about the truth she may come asking for her share in her father's money, which was all set to go to his wife in the form of a trust.

Emma's father turns out to be a good man and promises to be there for his daughter. He also helps Beckett get her job back at the NYPD as the commissioner is his golf-buddy. Castle gets back at 12th precinct as the consultant. Castle and Beckett kiss as Beckett puts on her badge, the next morning.