Beckett (Stana Katic) and Castle (Nathan Fillion) investigate the murder of a relationship guru to the rich and famous with a private jet on standby and whose car and office were both ransacked by a legendary fixer (Anthony Ruivivar). With no proof connecting the man to the crime, or any idea what he was sent to retrieve, Ryan (Seamus Dever) and Esposito (Jon Huertas) talk with the victim’s assistant (David Blue) and a wealthy former client (Dominic Hoffman) facing a messy divorce who arranged a secret hotel room for the victim in the days leading up to her death.
In the hotel room’s safe Beckett finds a 100 karat diamond the size of a baby’s fist worth $60, 000,000 which despite its size and clarity is unknown even by even by the diamond expert (John Hans Tester) the NYPD calls on to examine the stone. After Esposito and Ryan barely survive an armed attack by well-armed mercenaries, Beckett and Castle continue digging into the history of the stone and discover its owners (Jason Antoon, Tina Morasco) are clients of the dead therapist who refuse to claim the diamond (which Ryan learns is perfect, man-made, and actually worth far more than $60 million). Discovering the identity of the diamond’s creator leads Castle and Beckett straight to the murderer.
The mystery of the diamond holds quite a few false leads and twist and turns beginning with the fixer and ending with the reasons for the stone’s secrecy and the complicated true motive for the crime. “A Murder of Forever” also returns Maya Stojan as NYPD computer tech Tory Ellis in a pair of scenes to help identify and track suspects in the investigation. The episode’s B-story involves a small cohabitation disagreement between Beckett and Castle which, despite the writer’s initial refusal, eventually leads to Castle removing a prized possession from his bedroom to honor his girlfriend’s wishes.