|A Deadly Affair|
|Season 3, Episode 1|
|Air date||September 20, 2010|
|Written by||Andrew W. Marlowe|
|Directed by||Rob Bowman|
Beckett and her team burst into an apartment on a murderer's trail, only to be surprised when they find Castle, whom they hadn't seen or heard from in months, standing over the dead woman' body holding a gun. Beckett has no choice but to arrest Castle until he can prove his innocence.
- 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
- Molly Quinn as Alexis Castle
- Susan Sullivan as Martha Rodgers
- Michael Rady as Evan Murphy
- Lisa O'Hare as Kitty Canary
- Charlene Amoia as Ana Marie
- Gino Cafarelli as Dean Carbino
- Ethan Erickson as Xander Doyle
- Craig Gellis as Earl Moreland
- Justice Gamble as Bartender
- L.T. Tolliver as Uniform Officer
- Carolyn Ordoñez as Maya Santori
- Castle: You look good.
- Beckett: You look good too.
- Castle: Yeah?
- Beckett: For murder!
- Castle: You won't regret this.
- Beckett: I already do.
- "Fever (Adam Freeland Remix)" - Sarah Vaughan
- "Those Days" - Lucy Schwartz
- This episode is a mirror image of the previous episode, "A Deadly Game". In that episode, a murder appeared to be about an espionage conspiracy, but was really about an affair. In this episode, Castle and Beckett suspect fiancee Evan of committing the murder over an affair, but there was no affair: the killing was really about a counterfeiting conspiracy. Both cases featured glamorous secret lives: the spy game in that episode and the underground burlesque club in this one.
- In this episode, Castle discovers that Beckett broke up with Demming. Castle is still with Gina.
- Beckett loans Castle her gun, which he uses to shoot a suspect. This is a major violation of the law, which Montgomery (officially) overlooks. It's been previously established that while Castle does not have a firearms permit and doesn't own a gun (nearly impossible for a civilian in New York City), he is a slightly better shot than Beckett.
- Ryan shoots at Castle... but misses. Later, Castle refers to him as "Annie Oakley", a famous female marksman from the Wild West.
- While it might seem odd that Castle gestures right at Ryan through the one-way mirror (considering that Castle can't actually see Ryan), his long experience with interrogations would have allowed Castle to guess that Ryan would be standing in his usual place.
- Xander Doyle's name is a yet another reference to Buffy the Vampire Slayer (and its spin-off Angel), through the characters Xander and Doyle. Both were handsome "everyman" characters who the audience could identify with, and whose kept the team together emotionally.
- In a deleted scene, when Beckett is bent over writing on the murder board, she realizes that Castle is checking her out. She holds the pose for a moment, clearly happy he is attracted to her. When she straightens up, he's looking her in the eye. She's clearly conflicted about what to do next, but Ryan arrives before she can say anything. As aired, Castle's ungentlemanly look has been removed, and all we see is Beckett writing on the murder board, turning around, and sharing a significant look with Castle.
- Beckett's backup weapon is clearly seen in closeup when she hands it to Castle, and can be confirmed by the slide markings to be a Glock 26, the company's subcompact version of the Glock 19, which is one of the three pistols approved by the NYPD for carry.
- After Castle is released and returns home it is Alexis that reveals that Castle had planned on returning to the precinct after his book tour for Naked Heat.
- Castle's meth-related line, "Just like that cable show", references "Breaking Bad".
- Watch for: Beckett's face when Castle puts the coffee he bought for her down in front of her the day after she's let him join the case.