An investigation into the death of a subway worker reveals a child abduction.
- Almighty Janitor: Dean is basically this; his role as maintenance supervisor to the building he works in gives him access to every level of the building.
- Almost Kiss: After Alexis admits to Ashley she lost his pet rat, he forgives her after seeing how hard she tried to find him and goes in for a kiss, only to be cut off by Martha screaming.Castle: Found him.
- Chekhov's Gun: A subway worker talking about Len brings up a power system he had put within the subway to manage the power. When Beckett and Castle need to kill the lights to save Tyler, they find one such box by the room. Castle says it's like it was meant to be.
- Immediate Self-Contradiction: While Ryan is investigating the missing Dean Donegal, one of Dean's colleagues explains that she signed the man out sick when he didn’t call because the team have each other's back, but she then responds with exasperation when another person calls for her help.
- Laser-Guided Karma: The thieves killed Len in order to cover up the abduction of Tyler. As it's some of Len's own equipment to the subway system that allows Castle and Beckett to save the kid, it's almost like Len's laughing at these creeps from beyond the grave.
- Leave No Witnesses: Len was shot because he witnessed Tyler's kidnapping.
- Mistaken Confession: At one point, Castle and Beckett question Byron Singer - the owner of the surveillance equipment they found in Len's possession - about Len's death and believe that he's revealed Len was spying on a cheating partner. However, it turns out Singer and Len were birdwatchers; Singer claimed that he saw a pair of rare birds mating in the park and Len didn't believe it.
- Public Secret Message: When the abducted Tyler sends a video message to his father Dean, he says, "Don't forget to feed Ace"; since the family doesn't have a pet, the team realizes that this was actually a way to tell them that he's being kept in the subway tunnels at a point where the A, C and E lines intersect.
- Red Herring: The first ten minutes see the team investigating motives for killing Len Levitt based on his job, but once they find his camera, it emerges that he was killed because he witnessed a child abduction.
- Thriving Ex-Crush: Tyler's abduction leads to his father, Dean Donegal, a janitor, who was recently divorced and living in a small, one-bedroom apartment and "looking up at broke" after the divorce. Then Castle and Beckett meet his ex-wife, who married a wealthy doctor "before the ink dried" on the divorce papers. Dean isn't the murderer/kidnapper, however. His child was targeted because his job gave him an all-access pass to secure areas at a financial firm.
- Would Hurt a Child: The team swiftly conclude that the abductors would be willing to kill Tyler and Dean once Dean outlives his usefulness.
- You Have Outlived Your Usefulness: Captain Montgomery figures out pretty quickly that the robbers have no intention of letting Dean or Tyler live once their plan is through.
