Dale Tanner appears to be waiting for someone as he paces the sidewalk of a busy New York street. He notices a black sedan in the distance as he gets into his car. BOOM! Tanner's vehicle explodes in a firestorm. When Beckett tries to get close to the crime scene, Homeland Security shuts her down. She tries to talk to the two men who were doing surveillance at the time of the explosion. Castle thinks they look like the Men in Black. Agents J and K aren't talking. Beckett notices another mysterious figure casing the crime scene. She has no idea who this guy is.
Tanner's widow says her husband started a website for whistleblowers. He exposed lots of scandals and had a partner. Tanner's son, Sean, thinks his dad's murder will be covered up. The team learns that Tanner was having an affair with a security contractor who was trying find out who was leaking info about her company. This woman says his wife threatened to kill him when she found out about the affair. The widow insists Dale's work got him murdered. She may be right. The team learns that Dale Tanner's car was hit by a missile from a drone.
Castle and Beckett visit Fort Drummond to meet with the head of their drone program. The military men there give no answers to their questions. Everything is classified. Beckett recognizes the mystery man from the crime scene in another room. She promises she'll find out what's happening even though the feds have seized all evidence. The team uses a phone number they obtain from Sean Tanner to set up a meeting with the victim's partner, Omar, who says he was Tanner's assistant. Beckett subdues a man who is tailing them. He happens to be the mystery fellow she saw at the crime scene and at the military base.
The mystery man isn't talking. Beckett receives a call from the Attorney General ordering her to release her person of interest. No problem. She just needs some information in return. The mystery man is Stack. He's a special investigator for the Attorney General's office. He's there to objectively look into Tanner's death. He says the drone didn't come from Fort Drummond, but it did belong to the U.S. Someone hacked into it to blow up Dale Tanner's car. Castle believes this could be the rise of the machines. Beckett uses his theory to her advantage as she scares him with a remote control toy attack in bed.
Stack believes that a man named Simon Warburg is the only one who could have hacked the drone. The guy believes that drones will be used to attack U.S. citizens someday. Perhaps he was trying to prove this by killing an activist like Dale Tanner. Castle and Beckett track down Warburg by locating the bookstore where he shopped. There's a copy of Storm Season in the shopâ�¦ on the clearance table. Castle's crushed. As for the case, the bookstore owner points them toward Warburg's location. It's in an open field area where a small plane heads toward Castle and Beckett. It's coming in for an all-out aerial assault.
BANG! BANG! BANG! The plane fires on Castle and Beckett, so they fire back. CRASH! There's some debate as to who takes down the plane. Warburg doesn't care about that. He's just ticked someone shot down his drone (which was firing blanks, by the way). Warburg admits that his technology is what got Tanner killed. He knows that the next generation of drones won't have pilots. That means they'll kill without conscience or reasoning. He wants Dale Tanner to post his drone-hacking software to his website. That wasn't a great idea, as anyone with a computer could then take over a drone. Someone close to Tanner swiped the information though.
The prime suspect is Omar Dixon. Stack helps catch the guy before he skips the country. He lets Beckett do the honors of interviewing him. Stack is impressed with how she works. Castle notices this guy eyeing his partner. As for Dixon, he's not the killer. There's only one other person who could get close enough to Dale Tanner-his son, Sean. The kid was ticked because his dad put his crusade ahead of his family. He was pushed over the edge when he found out about his affair. Sean wanted to make his dad pay for what he'd done. Case closed.
Stack asks to have a private chat with Beckett. He wants to know what she has in mind for her future. Stack used to be a homicide detective, too. He sees bigger things for her. There's a job opening in DC with the Attorney General where she'd get to work on the most challenging cases out there. The stakes are high and the outcomes can affect history. Stack hands over a number to call to schedule an interview. Beckett promises that she'll think about it. However, she makes no mention of this intriguing job offer to Castle.