A body of a nanny stuffed into an apartment building clothes dryer sets off a convoluted investigation into the hows and whys of her death. Castle, now a part of the detective team through an arrangement with the mayor, lends his skills of envisioning scenarios and pointing out seemingly-unrelated details - not to mention unorthodox methods - to the investigation.
Police representative: Mr. Castle, be advised: if you get injured following Detective Beckett to research your next novel, you cannot sue the city. If you get shot, you cannot sue the city. If you get killed...
Castle: My lifeless remains cannot sue the city?
Police representative: Mr. Castle, these waivers are serious business. Perhaps you'd feel more comfortable by referring the matter to your attorney?
Castle: What, are you kidding? He'd never let me sign these! But fortunately, it's his job to get me out of trouble, and not to stop me from getting into it.
Ryan: So, she opens up the drier, takes the other person's clothes out, finds Miss Fluff and Fold here instead.
Esposito: If that's not a cautionary tale about poking around with someone else's laundry, I don't know what is.
Esposito: I'm sorry. If someone started rooting around my underwear without an invitation, I'm taking that as a serious breach of hygiene.
Kate: I thought you went commando, Esposito.
Castle: We could always make it strip poker.
Kate: Sorry, but I prefer mystery to horror.
Kate: (allowing Castle to join the detectives) It's accompany and observe. Not participate and annoy. Got it?
Castle: Participate and annoy's a lot more fun, but alright.
Castle: So. Looks like I managed to make it through the case without getting injured, shot, or killed.
At the end of the episode, Castle is typing on his laptop. He closes it and puts it on his desk. Seconds later, when he's looking at a photograph, the laptop is open again on the desk in the background. Then, when the camera is panning out, it appears to be closed again.
Beckett jokingly says to Esposito, "I thought you went commando, Esposito." This is a double entendre, but it's also literally true. Esposito is a former Army Special Forces soldier.
Watch for: a campaign sign during the park scene that reads "Jeff Horn for City Council". He's the next episode's victim. His opponent, who also appears in the episode, has campaign signs out as well.
Castle mentions the soap opera One Life to Live is where he got the idea for his first best seller.
Castle's comment to Brent Johnson that his voicemail recordings made "Alec Baldwin's messages sound like rainbows and unicorns" is a reference to Baldwin's 2007 voicemail to his then 11 year old daughter, in which he called her a "thoughtless little pig."