When two separate murders pop up, Castle bets Ryan and Esposito that he and Beckett can close their case first. Who says catching killers can't be fun?
There's a full moon out which makes for a wild night at the precinct. The team is called to a therapist's office where they find the body of Dr. Ashley Cosway. The doc's face has insults written all over it. Could it be the handiwork of an angry patient? A second homicide call comes in and Beckett sends Ryan and Esposito to check it out. The victim, Frank Anderson, is a retired school teacher seemingly shot during a random mugging. When everyone gets back to the precinct, Castle wagers that he and Beckett can solve their case first. Ryan and Esposito take that action. It's game on! But we're thinking all bets are off if Beckett finds out.
While Ryan and Esposito focus on gang kids who hang in the park where Frank Anderson took his walks, Beckett and Castle look into Hal Ross, a patient who has violent assaults charges on his record. Ross says that he's not their killer, but that Dr. Cosway got into a yelling match with whoever had the appointment before him.
Turns out Evan Hinkle, the guy scheduled for the aforementioned appointment, canceled and Dr. Cosway ended up having lunch with Jason, which means she was yelling at her hubby. As Beckett looks into this, Castle quietly takes bets from everyone else at the precinct. Beckett quickly figures out what's going on. However, once she finds out Jason took out a three million dollar life insurance policy on his wife, Beckett puts down a C-note on her and Castle. Ok, so we misjudged Beckett. Now we're just bummed we can't get in on the action.
Castle and Beckett interrogate Jason, sure he's their man. But when Ryan and Esposito hear Jason say he was at a basketball game, Ryan gets an idea. When Beckett and Castle emerge from interrogation, they see Ryan and Esposito watching last night's hoops game. Don't you just love "On Demand" television? They freeze frame Jason Cosway in the stands at the time of the murder. Think Vegas odds are shifting against Castle and Beckett?
The next day, Ryan and Esposito announce that they have a strong suspect in Eric, the son-in-law of Frank Anderson. Eric's been borrowing money from his father-in-law and Frank's apartment is rent-controlled. Eric ahs a solid alibi though. He was at a friend's birthday bash and couldn't have killed Frank.
Lanie calls everyone down to the morgue, as she believes both murder cases are connected. The same saltwater compound was found on both bodies, which is the equivalent of finding a matching fingerprint. Could the same person have killed both people? The team tracks down a suspect with connections to both victims. They quickly discover that he's on house arrest and couldn't have done it. In the gambling world, we call this a push.
A fingerprint leads them to the apartment of a paroled ex-con and his cohorts. The men swear that they had nothing to do with killing the victim. They only wanted the drugs inside him. They tell Beckett and Castle it was a client of theirs, Ron Bigby, who put them in touch with the victim. Esposito and Ryan bring in Bigby, who tells them that after losing his job, John Allen ran up significant gambling debts. In particular, he owed a large sum to a tattooed Russian whom he had played in a poker game.
Castle asks regular poker buddies Michael Connelly and Stephen J. Cannell for info on an underground high-stakes poker game. Castle crashes the game and is wired for sound and video. He's given instructions by Beckett to locate the tattooed Russian. After he locates the Russian, the plan is that Castle will leave the club. Think that'll happen?
When Castle gets inside, he sits down at the poker table teeming with tattooed Russians. Looking to flush out the killer, Castle tells the tale of John Allen and how he got involved with the wrong people. Watching from the surveillance van, Beckett sees that Castle has infuriated the real killer. He's the one twisting his prosthetic finger. Realizing that the killer will be going after Castle next, Beckett does a quick change into a hot outfit and works her way inside.
Castle wins the poker game but the killer is upon him before he can cash out. He forces him at gunpoint into the next room. Luckily, Beckett shows up pretending to be Castle's Russian girlfriend. We kinda dig her accent. She manages to disarm the killer and rescue Castle. Afterwards, Castle asks Beckett if she's too scared to look into her mother's case again. Angered, Beckett tells him they had a deal that he would leave her alone and she expects him to honor that. Beckett walks off, with Castle too stunned to follow her.
That night, Alexis arrives home upset. Her boyfriend forgot about their movie date and, even worse, he wouldn't apologize. As he comforts his daughter, Castle realizes his own mistake. He heads back to the precinct and apologizes to Beckett for violating her trust. As Castle walks away, Beckett tells him she'll see him tomorrow. It's just enough to let Castle know they are a team once again.