Castle and Beckett investigate the murder of a popular couples' and relationship therapist. At first they believe the killer might have wanted her high-profile client list. Though, after further investigation it seems that he was after a rare, and pricey object that was in her possession.
- Action Duo: Ryan and Esposito cover each other when they got attacked by a strike force.
- Artistic License – Geography: Dr. Peters says there are no diamond mines in the United States. There is the Crater of Diamonds Mine State Park near Murfreesboro, Arkansas, where guests can actually dig for diamonds.
- Call-Back: You know how Castle went seashell gathering with Beckett the first time they went to the Hamptons? Turns out he kept them and ended up framing them to replace a portrait of a lion that Beckett found unsettling.
- Deadpan Snarker: Aside from the usual cast diamond expert Dr. Peters is looking to compete.Esposito: How deep would my pockets have to be to afford this?Peters: Detective, you are not tall enough to have pockets that deep.
- Everyone Has Standards: Mr. Warner is horrified to learn his wife was the one who killed Alice for the diamond.
- Thou Shall Not Kill: While Hawke may had done a lot of questionable things as a spy, killing isn't one of them.
- Well-Intentioned Extremist: Alice was working with her boyfriend to bring down the international diamond cartel and to do is that is to steal a synthetic diamond from the Warners to prove that the ability to make perfect diamonds exist.
