Dr. Valerie Monroe is found dead in a coffin. We know, we know. What's so unusual about that? Well, Dr. Monroe was stuffed inside a coffin at someone else's funeral. An empty syringe was plunged into her carotid artery causing a fatal air embolism. Someone with medical training may have been the killer.
Dr. Monroe had a private meeting with a nurse at her hospital. Castle has seen enough medical dramas on TV to theorize that the nurse is probably hot. Beckett asks if he'd like to revise his theory when they meet Greg McClintock, the smooth-talking male nurse who was scolded by the victim for being too flirty with the female residents. Greg may flirt with every female doc on staff, but he hasn't slept with any of them. He also has an alibi and says he saw his boss leave the hospital with a mystery man.
Several nights a week, Dr. Monroe spent the night at a hotel suite belonging to a brutal drug lord named Cesar Calderon, who is a huge fan of Castle's work. Calderon employed Monroe as his private physician for his bad heart. The drug lord's brother, Manuel, says he dropped off Valerie at a diner where the mystery man mentioned by Nurse Greg was often waiting.
The guy that Dr. Monroe met with is Leonard Maloney of the Attorney General's office. She was working for him in an undercover sting investigating misappropriation of funds at her hospital. Monroe discovered evidence of prescription fraud and a possible smuggling ring.
Dr. Monroe's investigation led her to a women's prison upstate. Nurse Greg has been making weekly visits there to an inmate named Amy Porter, who has just had a stroke. Guess which hospital she's sent to for treatment? Castle and Beckett are shocked to learn that Amy Porter died while having an MRI. Or did she? The corpse at the hospital does not belong to Amy Porter. Nurse Greg switched the bodies. This was a prison break!
Nurse Greg charmed an unwitting hospital staff in order to get signatures on the medical orders and release papers needed to help Amy escape. He smuggled in drugs to simulate a stroke and fake Amy's death to switch her body with one from the morgue. Love letters lead Castle to believe that the fugitives may revisit the place where they first met – a Burgeropolis restaurant in Jersey. Hey, can we get some fries with that prison break?
Greg is captured and claims Amy was in prison for a crime she didn't commit. He happens to be right, so Beckett helps the couple out once she realizes Greg didn't have anything to do with the murder. During his chat with Dr. Monroe, Greg noticed her special bracelet. Castle and Beckett recognize the jewelry's design in a photo. It matches a necklace that Cesar Calderon wears.
Nylon fibers found on the victim's body match the carpet the sits inside the back of Calderon's Coupe de Ville. The drug lord admits he gave the doc his mother's old bracelet, but maintains that he was in his hotel suite when Monroe was killed. He then realizes that his brother took the keys to the car that night.
Manuel Calderon killed Dr. Monroe when she realized that she was working with the Attorney General's office. He was worried she was informing on his kin. When Cesar gave the doc his mother's bracelet, Manuel realized that his brother was too blind with love to see the truth. Manuel used the syringe skills he developed caring for Cesar to murder Dr. Monroe. Case closed.
In other news, Castle gets a little miffed when Gina steals his thunder by getting Alexis some sweet Taylor Swift tickets. He realizes that he was being a jerk and later apologizes. Gina then lets Alexis know that the tickets were from both of them. It's a nice gesture that impresses Martha.
Martha refuses to get sucked into her son's love life, but does pose a question after hearing about Nurse Greg's efforts to free his innocent girlfriend. Martha says, "When you come right down to it, would you be willing to break her out of prison? Because that, my boy, is true love." Castle has to ponder this. But when a similar hypothetical is presented to Beckett, the response is almost immediate. Beckett says, "Don't worry, Castle, I'd get you out." We believe she would, too.