[This is a review of Castle Season 6, Episode 8. There will be SPOILERS.]

Diamonds are a girl’s best friend. Unless you are a girl who stumbles upon a secret about diamonds and takes it upon herself to track said diamonds down to their source. Said actions might put you on the radar of the keepers of that secret and you might end up dead as a result. In which case diamonds are a terrible friend and you’re better off leaving the detective work to the professionals.

Such is the sad saga of tonight’s Castle, though to be fair, the story goes a little bit deeper than that.

At the end of the day, ‘A Murder Is Forever’ could care less about diamonds and cartels and creepy, teflon-coated private eyes. It’s a case study on love. And the crazy, stupid things we do for it.

Case Study # 1: The Warners. Husband Steve (Jason Antoon) gets the whole ball of wax rolling when his marriage goes sour. While most rich men would head to Tiffany’s, this one breaks out his chemistry set and just happens to have the mother of all breakthroughs in the diamond industry. It spirals out of hand as the greed takes over, but the starting point is love.

Meanwhile, wife Janet (Tina Morasco) loves her husband and their family’s reputation. Killing Alice is a byproduct of her desire to protect both of these things. As is the strike team hit she orders on Ryan (Seamus Dever) and Espo (Jon Huertas).

Case Study # 2: Alice and her boyfriend, Leo (David S. Lee). He might be on Interpol’s most wanted, but the story he spins for Beckett (Stana Katic) is one of young lovers and a shared hatred of the Cartel. They’re torn apart, yet time and distance don’t stop them from working together toward the same end.

It’s Leo who discovers the manmade diamonds and Alice who tips him off to the Warners as the source. Leo pulls off the snatch and grab, while Alice pays the ultimate price for trying to change the world and standing up for the cause of the man she loves.

Case Study #3: Castle (Nathan Fillion) and Beckett. If you are going to throw hints of tension into a relationship, best to do it against the backdrop of a murdered relationship therapist for the rich and famous.

Not that there’s ever any real tension beyond the natural kind that comes when two disparate lives begin to blend into one. Makes for some snappy banter between the two of them, though, and in the end the world’s oldest boy-man grows up just a smidgen and lets his romantic flag fly high.

So how did you like it? Did you enjoy the reprieve from the father/daughter angst? Would you like to see Hawke (Anthony Ruivivar) return to clash wits with Kate in another case? How does Castle’s grand gesture measure up? And who does wear the pants in the Ryan/Espo ‘ship?

Castle returns next Monday with the all-new “Disciple” @10pm on ABC.