A twist arises in the case of an art dealer found shot to death in his art gallery when a man with amnesia arrives at the station carrying a book with a bullet lodged in it that was fired from the same gun as was used in the murder. To solve the crime, Castle and Beckett have to jog his memory and unravel a possible connection to a high-level Arabian diplomat.
- "Ass" in Ambassador: A borderline case; Harun is arrogant, somewhat sexist and flexes his immunity but does at least offer up any useful information he has to the police when he didn't have to.
- Amnesiac Hero: The suspect is Jeremy Preswitck, who suffered amnesia from a murder attempt.
- Amnesiac Lover: Jeremy's ex-wife comes round to fill him in on his past and at the end, the two decide to give their relationship another go. As the team observes, one of them has years of baggage, the other is on a first date.
- Amnesiac Resonance: Discussed; the team initially attempt to determine Jeremy's name by having him sign his name as muscle memory may recall his signature (which allows them to give him the initial 'Jay' until they find his full name), and he later finds himself hitting it off with his ex-wife.
- Amnesiacs are Innocent: Discussed when Jeremy is arrested for the murder; the team are obligated to arrest him based on the available evidence, but Castle explicitly states that it's unfair that Jeremy be sentenced for something he doesn't even remember doing. Subverted when it's revealed he was framed.
- Chekhov's Gun: Or animal in this case. Before Castle enters the crime scene, he starts playing with a dog. He later realizes the dog must belong to the suspect when he realizes the plastic bags the suspect had on him was for picking up dog poop. Once Castle’s team track the dog at the pound, they find the pet’s collar has the amnesiac’s name.
- Crazy Cat Lady: A mentally ill patient posed as Jeremy's wife. Thankfully, Castle and Beckett figured it out as Jeremy had a serious cat allergy.
- Easy Amnesia: A downplayed example, at least for the easy. It's a combination of physical trauma (bump on the head) and psychological trauma (having been shot and thinking he's going to die) that leaves Jay with amnesia. The episode ends with Jay (Jeremy) having not recovered his memories and with no indication that he ever will.
- Meaningful Name: The art gallery owner is Victor Fink. A fink is a disgusting or contemptible person.
- Pocket Protector: Jeremy survived being shot in the crime at the art gallery due to the copy of Crime and Punishment he happened to have in his coat pocket. Ryan notes it’s lucky that Jay didn’t have a thinner book or he’d be dead.
