Ep 4. Number One Fan

In Castle Season 6 Episode 4, titled "Number One Fan," Richard Castle and Kate Beckett investigate a murder of a young woman named Mandy Michaels, who was found dead in her apartment. The investigation quickly takes an interesting twist when the detectives discover that Mandy was a huge fan of Castle and has even been writing a fan fiction story about Castle in her free time.

As they dig deeper into the case, Castle and Beckett discover that Mandy had been receiving threatening letters from someone claiming to be Castle's "Number One Fan," who is so obsessed with him that she is willing to kill to get his attention. With this new piece of information, the detectives start to suspect that Mandy's murder may be connected to this crazed fan and they race against time to find out the truth before she strikes again.

The investigation takes the detectives on a wild ride, leading them to different clues and possible suspects. Castle's wit and charm are on full display as he tries to solve the case and protect his beloved fans from harm. Meanwhile, Beckett shows her professionalism and her tough side while working to catch the killer.

The plot thickens as the two detectives come face to face with the Number One Fan, and the twists and turns keep viewers on the edge of their seats until the very end. With plenty of humor, suspense, and drama, Castle Season 6 Episode 4, "Number One Fan," is a thrilling episode that is sure to entertain and delight fans of the show.