Beckett has moved in with Castle! Okay, it's only temporary while her place is being fumigated. She's not the only one crashing at Castle's castle. His tornado of an ex-wife, Meredith (guest star Darby Stanchfield of Scandal fame), is also making herself at home to comfort an ailing Alexis, who was supposed to go on a Paris trip with her melodramatic mom. Beckett is ticked that Castle let Meredith stay with them especially after she gave him "the look." Thankfully, a fresh murder gives her something else to focus on for now.
Michelle Twohey was a divorce lawyer for the rich and famous before she took an ice pick to the neck. She had a note with the name "R. Garrison" on it and a Scarsdale address. Jane Garrison tells Esposito and Ryan that the "R" stands for her husband, Rob, who is a forensic accountant. Michelle was very anxious to meet with this guy. She was also desperate to hire her old photographer for one last job. There are lots of suspects in her murder, as the victim represented the wives of some of the wealthiest men in Manhattan.
Lanie gets a hit on some blood found on Michelle's jacket. It belongs to a disgruntled client named Samantha Voss (guest star Nancy Lee Grahn of General Hospital fame). The blood came from a physical altercation that wasn't as serious as murder. Castle and Beckett witness Samantha's penchant for fury firsthand when she destroys the high-priced items her husband, Walter, scored in their divorce case. The woman is violent, but she's no killer.
The team learns that the victim's boyfriend lied about his identity. They track him down through records at Esposito's alma mater, the University of New York. His real name is Noah Kesswood. He's a former military intelligence officer. He was likely spying on Michelle for another lawyer named Samuel Schuster, who represents pro golfer named Billy Piper (guest star Jack Wagner of Melrose Place and Dancing with the Stars fame). Billy's wife, Leann, disappeared at sea during a Caribbean boat trip they took to try to repair their marriage. Leann Piper was represented by Michelle Twohey. Coincidence? Nah.
Michelle may have discovered evidence that Billy Piper had his wife killed. That's a motive for murder. Billy claims his wife got drunk and fell into the ocean. It's an incident that cost him his career and reputation. Ryan and Esposito bring in Noah Kesswood, who was hired by Billy Piper to spy on Michelle. But he didn't kill her. Noah lets Beckett know that her murder victim was very close to finding out what really happened that night on the boat.
Ryan and Esposito can't believe their colleague let a woman he used to have "ex sex" with stay at his place. Beckett learns Meredith used to spike Castle's coffee with nutmeg to help him get through some all night writing sessions. She also learns that her boyfriend's ex wants to have dinner with her. Alone. Castle drives himself crazy wondering what these two ladies talking about. Beckett ends up having a great time with Meredith. She also lets Castle off the hook as far as being mad at him. Their makeup make-out session is interrupted by a break in the case.
Satellite photos show there were two boats in the area the night Leann Piper disappeared. One belonged to Billy Piper while the other was registered to Walter Voss, who actually has no real motive for murder. Mr. Voss did, however, make a call to the forensic accountant, Rob Garrison. Castle notices that Billy Piper's dead wife is actually a dead ringer for Garrison's wife, Jane. That's because they are the same person. Leann/Jane killed Michelle when she was going to expose the secret life she's been leading. Case closed.
Beckett is able to return to her apartment. Meredith is heading off to Paris. The two ladies share a private goodbye chat. Beckett asks Meredith why things didn't work out with her and Castle. The answer she gets is a tad unsettling. Meredith realized that her ex knew everything about her, but she knew nothing about him. For example, Castle always clams up when asked how he felt about never having known his father. That was a long time ago. Meredith says Castle is a totally different man now. The concerned look on Beckett's face suggests that she may not believe that to be true.