Kate and Rick enjoy a tryst at the loft on her lunch break. She’s been sneaking in through the building next door and then sneaking out again. When Kate says she has to get to a meeting with Gates at 1PP, Rick wonders if she’s really going to meet Vikram about LokSat. She assures him that when the time is right, she will loop him into the investigation.
As Martha rehearses for her new show, the dead body of Robin King, the theater janitor is found stashed in the fake snow. Robin was also an ex-con. Esposito and Ryan are on the case and Martha calls Castle and asks him to help find Robin’s murderer.
Turns out Robin use to deal drugs for Olivia Toussant, aka Mama. Robin delivered drugs to a high end party years back and decided to stay. Then she got into a car accident leaving the party and was arrested. When she got out of prison, Robin became a part of Scott and Linda Weinberg’s charity that helped ex-cons.
Alexis helps Martha cope with the loss of her friend by blowing bubbles at Castle’s P.I. office. Castle arrives with a a photo of the victim’s phone with a text message that was all emojis. The three of them work out that it’s a location and Rick and Alexis head over to check it out.
Rick and Alexis follow the lead and end up at a creepy warehouse. Rick calls Esposito and Ryan for backup, then he and Alexis stumble over a bunch of singers singing ‘80s music a cappella. Suddenly the police burst in and shut it down, based on Castle’s call for help.
Back at the 12th, Beckett pretends to be angry at Castle and slaps him in front of Ryan and Esposito. Later, the boys question Castle about he and Kate’s breakup and accuse him of cheating on her. Not knowing what else to say, he “admits” that he’s been dating a Russian model named Svetlana.
When Ryan and Esposito question Beckett about Castle’s cheating, she says it’s for the better and that she is also dating someone else, a Dr. Livingstone. Ryan and Esposito are crushed that their friends are no longer together.
The investigation continues and it turns out that Robin and a group of other ex-cons had entered into an a cappella competition. They fired Agnes Molina from their group when they didn’t think she was taking it seriously enough. Agnes says she was upset but that later Robin called her and asked if she’d meet her at the theater because she needed some protection. Agnes was late, and didn’t see Robin when she got there.
In order to get one of the other a cappella singers to talk to the police, Esposito sings a cappella. Robin found out that a competitor had bribed Dr. Larsen, the man in charge of the competition to keep Robin and her group out of the competition. Dr. Larsen was happy to do it as he felt that Robin’s group didn’t belong there because they were ex-cons.
While looking at video of Robin at the party where she got arrested, the detectives figure out that Linda Weinberg was at the same party. It turns out that Linda was high and left Robin to take the fall for the accident. Then she and her husband started their foundation to try and make up for it. Robin figured it out and went to confront Linda but ran into her husband instead. He offered to have Linda meet her at the theater to talk but instead, he shows up and kills her in order to keep their secret.
Beckett sneaks back to the loft to have more alone time with Castle and pretend to be his Russian model.