Alexis volunteers in a criminal review organization to help prove that Frank Henson was wrongly accused of murder 15 years ago. With his execution scheduled in three days, Alexis asks her father to bring a new look at the evidence.
- Amnesiacs are Innocent: Discussed and subverted; Castle and Alexis realize that Frank is covering for his younger brother John, who suffered minor brain damage years ago and apparently genuinely doesn't remember committing the murder. It turned out someone else killed the victim and John just found the body before Frank showed up.
- Big Brother Instinct: Frank spent years sitting on exculpatory evidence because he believes the real killer is his younger brother.
- Blended Family Drama: Beckett expresses her worry to Lanie that Alexis didn't go to her for help with the case, which ties into a general worry that she'll always be an outsider to Castle and Alexis's family unit. She and Alexis do have a private conversation at the end of the episode that ended in a hug which appears to have addressed those worries.
- I Never Said It Was Poison: When Alexis comes to Castle for help with the case, Castle mentions the accused's name despite her never mentioning it, revealing to Alexis that he was still checking up on her despite their estrangement.
- It's All My Fault: Frank is willing to be executed for a murder he didn't commit because he thinks his brother committed the crime as a result of brain damage sustained in a car accident Frank caused years ago.
- Once More, with Clarity: Only after John is questioned by Beckett does Frank's flashback show what he really did that night: he found his brother over the victim's body and thinking that John did it, he orders John to run while he tries to wipe down the evidence before getting caught by the police.
- Rewatch Bonus: The motivation for Officer Lane's confrontation of Castle and Alexis at the restaurant becomes a lot more sinister once it's revealed that he's Kim's actual killer.
- Screw the Rules, I Have Connections!: Lanie manages to expedite the testing of the sample sent to the lab because she knows someone who works there who agreed to test it after hours.
- Screw the Rules, I Have Money!: Castle bribes the librarian into checking who borrowed two old chemistry textbooks found at the crime scene by offering to make a donation to the library.
