Castle wants Pi out of his loft pronto. Alexis agrees he's been there too long. So she and Pi are getting their own place. Castle is against this big time. Fortunately, there's been murder to take his mind of his problems at home. A parole officer, Shauna Taylor, was tortured and killed in her apartment. A suspect was seen fleeing the scene covered in blood. The victim's stepbrother, Dr. Malcolm Wickfield, says Shauna felt like someone was stalking her. It could be a guy who approached her a few days ago saying that the fate of billions are at stake. The suspect is Simon Doyle. He says he's from the future. Castle says, "This just became my favorite case."
Simon is from the year 2035. There are energy wars in the future that allow for time travel. Someone made an unauthorized jump back in time. Simon was trying to prevent Shauna's murder because energy changes in the time stream began at the victim's apartment at 12:58 am. He believes the person who killed her did so because she has something he needs. Beckett isn't buying any of this. Castle thinks it's a great story. Ryan feels it's a bit derivative. Esposito adds that it all feels like a mash-up of 12 Monkeys and Terminator. Throw in a flux capacitor and Back to the Future would fit, too. And if there was a TARDIS...
Lanie determines that Shauna died around one-more accurately-12:58. This is the number Simon mentioned. According to the timeline, he's not the killer. Simon was locked up on a psychiatric hold during the murder. A high-end prostitute who was hired to cozy up to Shauna was ordered to steal her keys. Her pimp says the man behind this is Garrett Ward, a scary guy he met in prison. He often talked about a mission that would change everything. He's an anti-science freak. As for Simon, he's gone. All that's left in his cell are the handcuffs that held him. There's a chance he may have been recalled back to the future.
Garrett Ward once tried to detonate a bomb at a conference where Malcolm Wickfield was speaking. That's why he needed Shauna. He was trying to track down her stepbrother. By the time Castle and Beckett realize this, they are too late. Malcolm Wickfield is dead. His wife confirms that Ward is the killer. She also says he was looking to find "the child." She says some people hated her husband for trying to create a new energy source. The outrageous fear that something like this could create a black hole in the universe could drive a paranoid anti-science person like Garrett Ward to kill. The guy talked as if he was from the future.
Castle and Beckett track down Ward at a closed down power plant. They are surprised by the guy. Beckett is knocked out and Castle is choked violently. Thankfully, Simon Doyle shows up to scare the killer off with some device he holds in his hand. He, again, vows that he's from the future. He even knows that Castle and Senator Kate Beckett have three kids. He read it on a book jacket. It wasn't for a mystery novel though. In the future, it seems Castle takes on some serious literature. As for the case, Ward isn't looking for a child. He's hunting "Paul DeChild," a student who once wrote a letter to Malcolm Wickfield. Mrs. Wickfield has the note.
The letter matches a photo of the coffee-stained note Ward was using to track down DeChild, who, according to Simon, creates an energy field in the future. If the kid dies in the present, that shield will not be created and billions will die. Paul DeChild is enjoying a show at the planetarium. Ward knows he's there. He's about to take him out when Esposito and Ryan storm the theater. They neutralize the suspect before he can harm DeChild, who was the one responsible for stopping Ward from bombing that conference six years earlier.
Garrett Ward was once in a psych ward with Simon Doyle, who claims that event was just part of a clever plan that hasn't actually happened yet. Time travel really messes with your head. This is evidenced by the fact that Castle believes Simon has disappeared before his very eyes and Beckett spills coffee on the note that had the stain on it already in a photo. Again, time travel messes with your head. So does life in the present for Castle, who is still trying to come to terms with Alexis moving in with Pi. He's just not ready for something like this-even if his daughter is. For Castle, all this is happening way too soon.