The death of a recycling company employee, Sam Parker, becomes complicated with the discovery that the man had both a wife and a fiancée, and was apparently engaged in corporate spying. Meanwhile, Alexis takes an internship and is trying to return some misplaced personal effects from the evidence locker to a victim's family.
Tropes:
- Ambiguously Evil: Sarah is implied to be a professional corporate spy and was working for the actually-corrupt Carlsberg to manipulate Sam and sabotage his spying, but doesn't seem to have known about Carlsberg's illegal chemical dumping and in her eyes was likely just trying to countermand a genuine, unjustified spy. She did break into Sam's house trying to steal files which would have incriminated Carlsberg but it's implied that she didn't know what was in them and was just sent to do so by her boss.
- Bitch in Sheep's Clothing: Lance Carlsberg comes across as a Benevolent Boss working to save the environment and being victimized by spies when really, he's a Corrupt Corporate Executive dumping the battery sludge rather than storing or recycling it and killed Sam.
- Cat Fight: Between Sam's wife and fiancée, to Castle and Ryan's excitement.
- Corrupt Corporate Executive: Sam's boss Andy Berman had him infiltrate a competitor to steal their trade secrets. He argues that they'd been stealing his customers while refusing to share a formula that everyone could do good things with and he had no other choice. And with the reveal the formula was a fake and Carlsberg was just dumping the battery acid into the ocean and killed Sam, he makes Berman look practically saintly.
- "Eureka!" Moment: When trying to figure out who the misplaced personal effects belong to, Castle mentions Alexis could do work before she retired from interning. This makes her realize the detective who could've worked the case is retired.
- Feed the Mole: It gradually transpires that Sam was deliberately being given incomplete parts of the recycling formula that would do his employer no good. Not that there was a real formula anyway.
- Glamorous Single Mother: Sarah is revealed to be one, having a six-year-old daughter, with her alibi for the murder being said daughter's dance recital.
- Greenwashed Villainy: Carlberg claims to have found a method to recycling batteries safely, but in truth, his company simply switches the labels containing the battery sludge and dumps them in the sea. Sam Parker had discovered this while committing corporate espionage and was killed by Carlberg to silence him. The police are able to nail Carlberg when they find the gun he used to kill Sam in the dumpster outside of his apartment building, prompting a joke from Castle that Carlberg would have gotten away with it if he recycled.
- He Knows Too Much: Turns out there was no secret to battery recycling: New York Recycle was switching labels and dumping it in the ocean. When Sam found out about it, Carlsberg killed him when he couldn't buy his silence.
- MacGuffin: The formula for the cheap recycling of battery sludge. Which is a fake.
- Ms. Fanservice: In the prologue, a girl living in a New York apartment wanders into the hallway to throw away a pizza box... barefoot in hotpants and a tank top, as girls in New York are wont to do.
- Obnoxious In-Laws: Sam had borrowed money from his brother-in-law without paying it back and was also keeping big secrets from his wife, that guy's sister.
- Right for the Wrong Reasons: Helen denies having known about Sam's other apartment and says maybe Sarah is just trying to send the cops on a wild goose chase by claiming to have seen her there in order to keep them from looking into her as the possible murderer. Sarah did lie and send her the cops on a wild goose chase, but it was to cover her counter-espionage activities rather than her being the murderer and trying to hide that.
- Screw the Money, I Have Rules!: In the end, despite his spying, Sam remained true to his environmentalist ideals, rejecting a bribe to keep Carlsberg's chemical dumping secret and was killed for it.
- Secret Other Family: Sam had a wife and kids but was apparently willing to seduce and get engaged to Sarah as part of his spying, except she set that up to Feed the Mole and says that he never slept with her, using the excuse that he wanted to wait for marriage.
- Tempting Fate: The killer boasts that they have no evidence right before being presented with the murder weapon.
- Was It All a Lie?: Sarah, the fiancée, becomes depressed upon realizing that Sam was likely only seeing her to spy on her. It's an act, she was a spy leading him on too.
