A flustered Detective Kevin Ryan enters a restroom. He has blood on his shirt. He punches the mirror in a fit of frustration. We jump back six hours to learn that Ryan got another moonlighting security gig with his brother-in-law, Frank Kelly. The subject he’s been hired to protect is Congressman Alex Lopez. His wife Mia and his Chief of Staff, Megan Brooks are also in the mix as they all head to the event involving a woman named Caroline Decker and her Pure Water Now project.
Billionaire industrialist Carl Shelton lets Lopez know that he’ll never be president. A short time later, Lopez asks for some alone time with Carolyn Decker. Ryan is keeping an eye on the two of them when… BANG! BANG! BANG! Gunshots ring out. Lopez appears as if he’s going to survive. Caroline, however, is bleeding out. Ryan chases after a possible suspect, but loses him as the police arrive.
Ryan lets Frank know that the man he chased had a press pass. He gets a call from Beckett. Caroline Decker died in surgery. The case is now a homicide. Beckett meets the state party chair, Jim Boyce, who knows her reputation. She then meets up with Lopez, who remembers seeing a man in a grey suit. It matches the color of the suit worn by the guy Ryan chased.
The grey suit guy is identified as a political activist named Eric Chambers. Ryan and Esposito track him down. Chambers isn’t talking, but the fact that the gun used in the killing may have been inside the venue before he arrived, suggests he has an accomplice. A hotel employee saw Carl Shelton chatting with Eric Chambers.
An updated ballistics report suggests that Caroline Decker may have been the real target. Ryan calls in Castle for help with his theory that Eric Chambers is not the shooter. He learns that Shelton may not be involved in the killing. Chambers got his press pass from an anonymous source. Video surveillance footage shows someone placing the pass in his mailbox. Ryan recognizes the individual as his brother-in-law, Frank Kelly.
Ryan confronts his sister, Gwen, about what her husband may be into these days. He learns that extra money started coming in recently. That’s because Frank has been slipping press passes to outside parties for profit. He claims he didn’t kill anyone and refuses to turn himself in. Ryan has no choice but to arrest his brother-in-law.
Beckett finds a second phone owned by Caroline, who was having an affair with Lopez. His wife, Mia, becomes a prime suspect. But the real killer is his Chief of Staff, Megan Brooks who feared being cast aside when Lopez made his run for the presidency. Case closed.
At the station, Castle learns that Beckett is studying for the captain’s exam. Elsewhere, Ryan brings his brother-in-law home. Ryan advises him to tell his wife the truth. His sister is stronger than he thinks. Gwen opens the door to their apartment. She gives her husband a hug assuring him that they’ll get through this crisis. Ryan gives his sis a knowing nod before heading back to his own family.