Alexis doesn't care for her dad's new character. He's a robbery detective named Schlemming. The guy comes across as a bit of a doofus. This brings a smile to Castle's face. See, there's this handsome real-life robbery detective name Demming who has been spending a lot of time with Beckett, professionally and personally. Castle needs a good murder to take his mind off his heartache. Fortunately...
Damian Wilder, CEO of a men's skin care line, took a bullet to the chest. That's not what killed him though. A bloody art object lying on the floor indicates he was bludgeoned to death. There's a smashed glass case and the word "Murdere" written in blood on the wall mirror. A broken clock helps determine the time of the crime.
Tom Demming (aka Schlemming) sits in as Beckett and Castle interview Wilder's cousin, Blake, who says the items stolen from the cases were rare first edition books. Blake matches the description of a person seen dumping the collectibles. But an ATM transaction has him withdrawing cash in the middle of the murder timeline window. He can't be their guy.
Castle realizes that the message on the mirror was unfinished. The killer meant to write "Murderer!" Wilder's company VP Lisa Jenkins says they were under fire for product testing. Animal activist lance Newman admits to vandalizing Wilder's stoop with paint when he heard the victim in an argument with a woman. It could be the same person he was meeting at a sleazy hotel. A phone call to the room came from Wilder's office. It was made by VP Lisa Jenkins, but security footage has her returning to her apartment building in the middle of the murder timeline. Lisa couldn't have done it either.
A hotel clerk found a duffle bag with $75,000 under the bed in the room Wilder visited. Beckett, Castle, and Demming put the facts together: a duffel bag full of cash and an anonymous motel room - it wasn't an affair, it was blackmail. All signs point to a lab tech named Rebecca Strong as the extortionist.
Only Beckett can understand the words Rebecca utters between sobs. She says, "It's cry talk. There's not a girl alive who hasn't heard it from a sobbing, heartbroken girlfriend." Rebecca says that Wilder's company had come out with a product that had a chemical that causes capillary damage. She tried to tell her superiors but they ignored her. So, she blackmailed Wilder for money. In fact, she still has the cash! Apparently, there were two payoffs for the same blackmail. Rebecca didn't notice the second bag that was later swiped by the clerk.
Damian Wilder wanted to do the right thing by issuing a product recall. Cousin Blake would have company stock worth a fortune from when he lent Wilder the start-up money and VP Lisa would be looking at criminal liability if it got out that she let a dangerous product go to market. But the timeline rules both of them out.
Beckett deduces that Lisa came in, shot Wilder, and started using his blood to write the message on the mirror to make it look like activists did it. But before she could finish, she heard Blake coming to kill Wilder and fled. Then Blake finished Wilder off by bludgeoning him to death. He stole the books to make it look like a robbery gone wrong. Lisa and Blake both came to kill independently and inadvertently alibied each other out. One murder - two killers.
Now, remember how we said Beckett and Demming were spending a lot of time together? Well, that relationship has clearly been taking its toll on the typically cool Castle. He spent the entire investigation trying to one-up the charming robbery detective. Demming was also doing his best to crack the case before the equally charismatic Castle. Now, some may argue that this was all done in their never-ending pursuit of justice. But we know these two guys were going all out in their pursuit of Kate Beckett.
At the end of the day, Castle wants to congratulate Beckett for cracking the case. He finds her in the precinct hall, but she's not alone. She's holding hands and sharing a kiss with Demming. Castle looks like he's just been punched in the gut. It's obvious he has strong feels for Beckett. It's obvious that Demming does, too. The question is: Who will get her in the end?