Castle

Opens with a body going round and round in a tumble dryer.
Castle is signing a waiver at the station saying that if he gets injured, shot, or killed, following Det. Beckett to research his next novel, he cannot sue the city. Beckett gets a call and Castle asks if they have a case. Beckett says that they don't have a case, she does. He has paperwork.
In the laundry that the body was found in, Det. Ryan explains to Beckett that Mrs. Rosenberg from 9E found the body. Beckett takes in all the evidence in the room while Ryan and Esposito argue over laundry room etiquette. The girl in the dryer works in room 12F, she's the nanny.
Beckett takes the elevator up, only to find Castle waiting for her on the 12th floor. Beckett asks how long Castle's going to be following her around. He says that it's hard to say how long it'll take for inspiration to strike. Beckett says that his inspiration might strike him sooner than he thinks.
Castle tells Beckett that the nanny's name was Sarah Manning and she was with the Petersons for about 2 years, when Beckett questions where he got his information from, he gloats that the door man is a huge fan of his work.
Beckett questions the Petersons about Sarah, what she was like and her daily schedule. Castle asks whether she had any boyfriend problems. Sarah broke up with her boyfriend about a month ago. Beckett thanks them for their time, and tells Castle that they're leaving.
Out in the hall, Castle complains that he had a lot more questions, she says that she likes to investigate things herself first. Beckett looks through Sarah's handbag for her phone so she can call her parents, but the phone isn't there, Castle says that it might be in the laundry room, or the dryer.
Ryan and Esposito show Castle, Beckett and the Captain security footage from the elevator showing that the perpetrator must have used the stairs to get in and out of the laundry room. Ryan says that he'll run the three maintenance workers who were on duty, Castle asks why not run all the neighbours' names, seen as the neighbour as a killer would make a better story. Castle then tells a tale about the guy in 8B and how he stalked a pretty girl. The Captain tells them to find out more about the neighbours and find out who lives in 8B.
Castle comes home to find his daughter Alexis cleaning up after his mother Martha has made Chicken Marsala for dinner, then taken a "dramatic pause" when it came time to clean up. Alexis asks who got killed today, and when Castle says that it was the nanny, she asks why she never had a nanny. Castle explained that her mother and he decided that if anyone was going to screw her up, they wanted it to be him. When Martha comes down from her dramatic pause, Castle reminisces about his nannies, only that they weren't called nannies, they were called alcoholics, raving lunatics and completely irresponsible middle aged women. Castle gets a phone call, Beckett calls him for an autopsy because she was ordered to, not because she wanted to.
Lanie explains that Sarah died when her head hit the table after she was hit with a bleach bottle. Lanie also notes that Sarah had sex within the hour of being killed, possibly within minutes, and the evidence points to the fact that she knew the guy.
They bring in the ex-boyfriend for questioning. Beckett and Castle question him about why they broke up, and showed him some threatening messages he left on Sarah's phone. He starts telling the truth and it comes out that Sarah had a friend in the building, another nanny.
Beckett and Castle go to the playground where Sarah and her friend Chloe used to take the kids and Castle talks about how he used to take Alexis to the park every day. Beckett says she never figured him for "Mr. Mom". They question Chloe about the person Sarah was seeing, Chloe seemed to think that it was Mr. Peterson.
Beckett and Castle question Mr. Peterson about Sarah, it turns out that he was having an affair, but not with Sarah. Sarah was covering for his affair though.
Back at the station, Ryan says that Mrs. Peterson wasn't where she said she was the day Sarah was killed.
They go and question Mrs. Peterson, she said that she lied about where she was because she was with her lawyer filing for divorce.
Castle steals a copy of the elevator footage and watches it at home looking for Sarah's phone. He figures out that Sarah travelled to a couple of different floors.
Castle demonstrates how he figured it out to Beckett, and says that the guy Sarah had sex with was probably on the 15th floor, so he starts knocking on doors. They find the family that Chloe nannies for.
Beckett and Castle question the family, Castle calls Sarah's phone number and they hear it ring from the bedroom. Sarah was having an affair with the husband, Ian.
They take him in to question him, he said that Sarah left his apartment a couple of minutes before Chloe got back from the park.
They check out the story with the elevator time stamp. It matches, but they see that Chloe is in the elevator without the kid, when according to Ian, she usually has the kid with her.
Beckett and Castle go to find Chloe at her apartment, she's not there, but they find a picture of the family she nannies for with the mother cut out of the picture.
They race over to the family's apartment to find Chloe before she does anything rash. When they get there, Chloe has already knocked Ian out, but she's not in the room anymore. The door man calls and says that they're a girl in the laundry room with a knife.
Beckett and Castle go in to talk to Chloe. She's cutting her leg with a knife, she seems distraught and somewhat suicidal. Chloe talks to Beckett about how she was sleeping with Ian while he was sleeping with Sarah, and how he said he loved her and was going to leave his wife for her, and that she is pregnant with his baby. Chloe had come down to the laundry room to talk to Sarah, but ended up hitting her with the bleach bottle and putting her in the dryer when she didn't get up. Beckett convinces Chloe to put the knife down.
Outside, Castle tells Beckett that he managed to get through a case without being injured, shot, or killed. Beckett says that there's always tomorrow. Castle says that he liked the whole sisterhood thing she ran back there, she says that she wasn't running anything, and that what the husband did was terrible, and he'll get away without penalty.
At home, Castle is writing about Nikki Heat and how her heart had once been broken. Alexis comes in and asks if they got the bad guy and thanks him for being her nanny. Castle takes out a picture of himself and Alexis when she was little and stares at it reminiscing.