In "Valkyrie," we learned that a chemical agent that was being developed for the military was stolen. Castle was exposed to the poison. Based on the amount found in his bloodstream, he has less than a day to live. Castle tells Beckett about a secret military base called Dreamworld. It could have something to do with the toxin. A reporter named Brad Parker tried to write an article about the place, but it was quashed by someone high up in the government. Bronson, the man who kidnapped Castle, may have been a source for the piece. Parker says Dreamworld is a training base for kill missions the Pentagon would prefer to deny ever took place.
Parker claims his story was axed at the personal request of Defense Secretary Reed, a military general who once ran all operations out of Dreamworld. If anyone has something to hide, it's him. So Beckett and her partner, Rachel McCord (guest star Lisa Edelstein), head off to the Pentagon. Defense Secretary Reed is less than forthcoming about revealing any details about Dreamworld. He does share that Bronson was part of a mission that took out Al-Qaeda's number two leader. It crippled the terrorist group's entire command structure. Beckett worries the chemical agent theft may be part of a forthcoming retaliatory strike.
Bronson once met with Waqas Rasheed, a cousin of the Al-Qaeda leader who was killed. The guy was there the night of the lethal airstrike. Beckett and McCord track down Rasheed, who claims he doesn't share his dead cousin's beliefs. He also says that Bronson was stalking him to find out if he talked to anyone about their secret. Rasheed saw him standing in the rubble holding a servant woman's dead body. Bronson threatened to kill him if he ever said anything about what he'd seen. Then he left with the body. Beckett's instincts have her thinking the guy is telling the truth.
Castle gets a shot that will stave off the poison long enough to give him about 10-12 hours before he's beyond help. He assures a worried Martha and Alexis that all is well, but his mother knows something is amiss when her son speaks to her minus his standard wiseacre quips. Martha wants Esposito and Ryan to find out what's happening. Back in DC, McCord assures Castle that Beckett is doing great. She also authorizes her tech guy to use back channels to get access to the actual recording of the missile strike. They hear Reed give the order to fire even though Bronson said they had an operative still inside. It was the servant woman. She was Valkyrie.
Beckett knows that Reed lied, but is ordered to steer clear of him. That's not going to work for her. Beckett attempts to question Reed at his home in front of his wife. Again, the Defense Secretary is less than forthcoming. The fact that Reed filed a complaint against Beckett leads her to believe he's not involved. Carl Villante (guest star Yancy Arias) is impressed at how his newest charge got this suspect to show his hand. Still, Reed was their only lead until Farrah Usman is identified as the servant woman/spy who was killed. She happens to have been engaged to Brad Parker.
Parker was doing his story to determine how his fiancée was truly killed. As a former vet, he knew her death didn't go down the way the government had claimed it did. The team realizes that Parker is going after Defense Secretary Reed for revenge. The race is on to find him, as well as the antidote for the toxin that's currently killing Castle. The clock is ticking. Castle and Beckett realize that Parker may not actually be going after Reed. He's likely be going after the person he loves the most. He's going after his wife.
Beckett and Castle race to Reed's house while the rest of the team continues toward the Defense Secretary himself. Parker meets with Mrs. Reed under the guise of doing an interview. As Beckett pulls up to the house, Castle collapses to the ground. Mrs. Reed is also unconscious inside. Beckett chases after Parker, but he gets the drop on her. Thankfully, McCord is there to back up her partner.
A short time later, Castle awakens in the hospital surrounded by everyone who loves him. Oh, and Alexis's new boyfriend, Pi, is also there. It's a joyous occasion nonetheless. Mrs. Reed pulls through, too. Her husband will likely not suffer any repercussions for his actions. That's just the way it is in DC. As for Beckett, she thanks her new partner for backing her up. Then she gazes down at the hospital room that holds her old partner, who also happens to be the love of her life.