|The Double Down|
|Season 2, Episode 2|
|Air date||September 28, 2009|
|Written by||David Grae|
|Directed by||Rob Bowman|
When Castle and Beckett are handed the murder of Ashley Cosway, a couples therapist, and Ryan and Esposito are assigned to investigate the death of Frank Anderson, a dead man found shot in a park, Castle makes a bet on which pair can solve their murder first. But when both investigations hit dead ends and the victims are found to be strongly connected, the two teams work together to solve the peculiar puzzle.
- Nathan Fillion as Richard Castle
- Stana Katic as Detective Kate Beckett
- Jon Huertas as Detective Javier Esposito
- Seamus Dever as Detective Kevin Ryan
- Tamala Jones as Dr. Lanie Parish
- Ruben Santiago-Hudson as Captain Roy Montgomery (credited only)
- Molly Quinn as Alexis Castle
- Susan Sullivan as Martha Rodgers
- Diana Maria Riva as Detective Roselyn Karpowski
- Arye Gross as Sidney Perlmutter
- Brennan Elliott as Jason Cosway
- Matt Winston as Evan Hinkle
- Gareth Williams as Wesley Grovner
- Amy Stewart as Brandy Rossi
- Jim O'Heir as Hal Ross
- Linara Washington as Christina Marx
- Marco Martinez as Eric Marx
- Dinora Walcott as Detective Mindy Stegner
- Brian Allen as Messianic-Looking Guy
- Castle: What is it about full moons that bring out all the crazies?
- Beckett: I don't know, you tell me.
- Castle: You guys should really sell tickets. I mean, you got everything. Madness, mayhem. Now all you need is...
- Lanie: Quit looking at the girls, Castle.
- Lanie: Looks like a patient lost his patience.
- Castle: Also his command of grammar. You're should be you-'-r-e- as in you are, that's not even a tough one not like when to use who or whom.
- Beckett: Do you really think that's the take away here, Castle?
- Castle: I'm just saying whoever killed her also murdered the English language.
- Esposito: A warm milk nightcap with your lady? That is sad, bro.
- Ryan: It helps her sleep.
- Esposito: How about the sound of your voice? Doesn't.... Works on me.
- Ryan: How you doing, Dr. Perlmutter?
- Perlmutter: Shhhh! The body is speaking.
- Esposito: What's it saying?
- Perlmutter: It's saying, "someone shot me."
- Esposito: Loser wears a dress to the precinct for a week.
- Ryan: And why stop there? Loser also shaves his head. Or are you chicken?
- Castle: You're on, honeymilk.
- Esposito: Honeymilk.
- Ryan: Damn it.
- Castle: It's a common mistake, but it's not ironic that Dr. Cosway's not here for you to lean on; it's just simply tragic. It would be ironic if her death made you feel better.
- Beckett: Betting on murder cases, guys? Really?
- Ryan: Whoa. What? No.
- Esposito: That would be wrong.
- Castle: I'm telling you, it's Girl Scout ord--
- Beckett: Girl Scout cookies are sold in February. You guys should be ashamed of yourselves, now get back to work.
- Karpowski: Beckett, you are not going to believe this.
- Beckett: Yeah, well the bar on unbelievable is pretty high right now.
- Karpowski: This husband took out a three million dollar life insurance policy on his wife last month.
- Beckett: (turns back to Castle) Hundred dollars on us.
- Beckett: Are we really rooting against solving a murder?
- Castle: Well, I don't want to shave my head, do you?
- Beckett: Why would I shave my head?
- Castle: You're in on the bet, aren't you?
- Beckett: Yeah, but I didn't realize...
- Castle: makes razor buzzing sound as he moves his hand over his head
- Castle: Could it be that easy? "You take mine, I'll take yours."
- Esposito: What are you getting at, Castle?
- Castle: Strangers on a Train.
- Ryan: The Hitchcock movie?
- Castle: I'm partial to the novel by Patricia Highsmith, but yes.
- Castle: "Bam" said the lady, there's our connection!
- "Who Taught You To Live Like That?" - Sloan
- "We Are Not The Losers (Anymore)" - Actionslacks
- Castle often jokes about bringing popcorn to events that promise to turn wild. On this full moon, he does exactly that.
- At the crime scene where Castle says, "You know, if this was one of those super science-y forensic shows, stick some electrodes in these fishes' brains. Get a fish-eye view of whatever they saw." is a dig at the crime show Bones (2005-2017). TJ Thyne plays Dr. Jack Hodgins, an entomologist, botanist, and mineralogist who is an expert on spores and minerals. He can estimate time of death from insect larvae in human and animal remains and is called "Bug Boy" in the series by Agent Booth. Dr Temperance Brennan was also an award-winning and popular novelist in the show, who wrote bestsellers, just like Castle.
- This is the first episode to feature Ryan's occasional nickname, "honeymilk". It refers to the warm milk and honey nightcap he shares with Jenny to help her sleep.
- Castle wonders how a killer who writes a message on the body of the person he just murdered could make such an elementary grammar mistake when the message is important enough to kill to send. While this seemed inappropriate when, it actually illuminates the case. The killer didn't care about the message at all; it was purely a red herring meant to throw off suspicion.
- Serendipity 3 is a restaurant on the Upper East Side of Manhattan that is famous for its ice cream desserts.
- Beckett says that this case is proof that any two people can be connected. Ryan draws a parallel to the movie, Crash, which centers on a group of unrelated people who all end up connected to one another. Castle compares it to Six Degrees of Kevin Bacon.
- This is a game that states any actor can be linked to Kevin Bacon by no more than six acquaintances. Nathan Fillion's "Bacon Number" is one. The two worked together in the 2010 film, Super.
- The game is based on the concept of six degrees of separation, which states that any person is connected to another through six acquaintances.
- Castle calls Beckett "Debbie Downer" when she says their suspect in the two cases may be a coincidence. The name refers to a character from Saturday Night Live from 2004, played by Rachel Dratch.
- The building that Castle and Beckett approach Mr. Cosway at when he is leaving to meet the movers at Ashley's office is actually the "Ninth and Broadway Building" on Broadway St. in Los Angeles, California.
- When Mr. Cosway says that he bought a slice of pizza at Ray's, Castle asks, "Original Famous or Famous Original?" This is a reference to coming events in Slice of Death, in where three pizzeria owners named Nick fight over who was the original Nick.
- The case hinges on the salt water compound, which was found in trace amounts on both victims. Later, the compound was confirmed not to have come from Ashley Cosway's office.
- The Hudson River is fresh water, not salt water. However, this episode is accurate in that around New York City, the water becomes brackish from emptying into the Atlantic Ocean. And as the tide comes in, the Hudson becomes salty for several miles upstream.
- There's proof that Beckett was a Girl Scout since she knows about Girl Scout cookie selling in February
- Alexis and her first boyfriend Owen broke up
- This is the first time two M.E.S work together in this episode