When we last left our favorite mystery man and his muse in "Watershed," Castle was down on one knee making a little proposal. Beckett is stunned. Her indecision on how to answer the question before her is amplified by the fact that she just got a top job with the Justice Department in DC. That's cool. Castle isn't proposing to keep her in New York. He's proposing because he can't imagine his life without her. A move will be tough, but that's something they can figure out. Beckett is relieved and beaming. She says, "Well, in that case, Richard Edgar Alexander Rogers Castle... Yes. Yes, I will marry you." Woo hoo!
Two months later, Beckett chases a suspect into an alley. BANG! BANG! BANG! Beckett is shot multiple times. Her partner, Rachel McCord (guest star Lisa Edelstein), chastises her for failing miserably during this training exercise. She suggests the Justice Department's newest recruit start using her instincts as opposed to relying on intel. She can start with her latest case which her boss, Carl Villante (guest star Yancy Arias), says could involve a potential national security breach. This puts Beckett's plans to spend some quality time with Castle in jeopardy. Speaking of her fiance...
Castle returns from a whirlwind book tour to find Alexis is home, and she's not alone. She bought some Pi. That's the name of the free-spirited guy she met in Costa Rica. Pi has made himself quite at home in Casa de Castle. Beckett, on the other hand, hasn't even unpacked the boxes in her DC apartment. She's thrilled when Castle surprises her, but not so happy about his desire to peruse the file on her classified case. If she truly didn't want him to snoop, she shouldn't have accidentally dropped a top secret photo before heading out the door.
Castle ropes in Ryan and Esposito in helping him make sense out of the evidence photo featuring a blown transformer that controls a 10-block region of Arlington. A blackout temporarily shut down the security system of a company called Cybertech Transnational. A module containing access to the military's satellite network was stolen. The thief could leave a large portion of the U.S. defenses disabled. Beckett believes the bad guys may have escaped underground to a golf course. Castle figures this out, too. That's why he's already snooping around the greens when Beckett and McCord arrive.
An unknown figure snaps shots of Castle at the golf course. Security footage shows a man doing surveillance for an escape route. It's a recently retired Marine named Bronson who worked Black Ops. A sweep of the guy's apartment comes up empty in the search for the missing module. Bronson is missing, too. That's because he's busy kidnapping Castle at gunpoint. Bronson wants to know if the feds know about Valkyrie moments before he passes out at the wheel of his speeding car. CRASH! Bronson is dead. Beckett and McCord are stunned to see an unharmed Castle at the crash site where he's promptly placed under arrest.
Villante knows Castle isn't involved with Bronson, but he wanted to scare him for info. There's nothing relevant about Valkyrie in their system. Bronson's girlfriend, Jeanette Miller, works as an aide to a ranking member of the Senate Foreign Relations Committee. They track down lady as she heads into Union Station. Beckett convinces McCord to hold off on arresting her. Instinct. The delay pays off as Jeanette leads the feds to a locker where the missing module is recovered. Jeanette claims she and Jack have been set up. She also has no idea what Valkyrie is. Beckett believes her. Instinct, again.
Beckett thinks the security module may have been a diversion so the bad guys could get to the 8th floor of the building where Cybertech is located. In other news, Castle returns home to find Pi making fruit-based meals in his kitchen. He takes his uninvited houseguest's advice to talk about his problems, with someone other than Pi, of course. His chat with Ryan and Espo segues into the case in Arlington. The subject of military ghost bases comes up. Castle is in the middle of doing research on this new lead when two federal agents show up at his door. They take him away without explanation.
Castle finds himself back in Washington. The feds take a sample of his blood. Beckett explains that something else was stolen from another lab in the Cybertech building. It was a chemical agent being developed for the military. It was deemed too dangerous to use. The amount that was stolen could kill thousands of people. It was aerosolized to kill Bronson in his car. Castle was also in the vehicle. Beckett says that based on the amount of the chemical found in his bloodstream, her fiance has less than a day to live.