DAY 4

The team now think Nick Johnston is the killer as it is confirmed he left work around 5 and came home around 7. Apparently he had seen Vivien the day she was murdered as witnesses confirmed a woman of Vivien’s description hanging around with Nick. The team theorise that Vivien must have worked out the affair and wanted to being Nick to justice that very day for killing Amelio.

Speaking to Nick later, they discover that he did go to Vivien’s office as she had called him and said she wanted to speak to him. Only when he got there, no one answered the door.

Nick did know about his wife’s affair and went to see Amelio to tell him to stop it, but Amelio said no, even though Nick threatened to tell Amelio’s wife.

Then Penny Marchand arrives, saying she knows who killed her mother. Penny says she had a dream last night where her mother was sitting at a table pointing at strange men and repeating: “Ask the Masons what happened.” Beckett is sceptical about this, but Castle thinks this could be a lead.

Beckett then turns her attention to the Carsillas mother and daughter though they have an alibi for that night as they were dining out at a fancy restaurant. Beckett is still suspicious and later finds out that the restaurant is close to Vivien’s office and that it is called Mason’s. Castle is excited as this means that Penny’s prediction is right. He begs Beckett to talk to the restaurant people.

Castle hands Beckett the restaurant card with Mason's written on it

 Later the Carsillas ladies are called back in for questioning. Marina tells the team it was her idea to go visit Vivien for closure for her father and that night her mother wanted to try Mason’s as it was a brand new place. Marina says this place was so new they didn’t offer a wine selection, so her mother decided to go to the liquor store to buy some wine. She was gone about 20 minutes around 5:15pm.

But Beckett says this is a lie and produces a receipt from the store which states that Paula bought the wine at 3:12pm and at the same time she also bought a brand new ice pick.

Marina cannot believe this and asks why she would do it. Castle explains Paula killed Vivien to cover up Amelio’s death. Paula explains that Amelio told her about the affair, so she started slipping pills into her husband’s coffee every morning. When she and her daughter started seeing Vivien, Vivien knew things about them she shouldn’t. 

That very night Vivien was going to commune with Amelio’s spirit and Paula Carsillas knew that her husband would tell Vivien how he was murdered. So she had to shut Vivien Marchand up for good. It must also have been she who wrote the letter about her death.

So Paula Carsillas was the killer.