The season finale of Citadel brings high stakes action, long-buried secrets, and a shocking betrayal that changes everything. The biggest mysteries of the season are solved in episode 6, and the stage is set for an even more complicated future.
A Serbian Tragedy
The episode opens in Serbia, thirty years before now. He sits alone, a young boy in a medical facility filled with wounded survivors. Doctors and nurses work around him.
Six months later, the boy is living with his grandmother in Oregon. He asks when his mother will come back, he misses his father but is told she is away travelling.
In the present, Mason looks back on his past, admitting he never really knew who he was until Citadel gave him purpose—and until he met Nadia.
What Does Dahlia Desire?
Nadia, Mason and Carter are taken to meet Dahlia in present-day Morocco. They want proof Asha, Nadia’s daughter, is still alive before they agree to anything. Dahlia has video evidence of that.
Dahlia explains her plan. They need to fly over the Pacific ocean, penetrate a nuclear submarine and capture its missile systems. Nadia volunteers to lead the mission and is about to head out when Carter drops a bombshell: years ago, Mason had put his own bio-lock on the sub during an off-the-books mission. If anyone can get in, it has to be him.
Mason’s Secret Assignment
A flashback takes viewers back to eight years ago. Mason is tasked with sneaking aboard a Russian nuclear sub and uploading Citadel access protocols.
Then Mason pressures Grace to get information on Nadia’s whereabouts before accepting the mission. He manages to upload his biometrics successfully while operating, but installs a secondary device in secret, cutting off communications for long enough to hide his activities.
Now that decision comes back to haunt him.
The Undersea Adventure
Carter discovers the sub back in the present. Mason and Davik parachute onto it but Mason is having trouble with the descent.
Mason’s biometric data unlocks the system and Davik decides that Mason is no longer useful. He fucks up Mason’s gear, sets him adrift before he cuts him loose.
Nadia realizes something is wrong and decides to take matters into her own hands. She fights off Dahlia’s men and she herself gets on the submarine.
Inside, Davik contacts Dahlia and tells her his plans. He knows Dahlia killed his brother. And he plans to use the missiles on Manticore families. Davik wants power in exchange for his cooperation.
Meanwhile, Carter manages to revive Mason, allowing him to rejoin the mission.
Nadia’s Race Against Time
Nadia must remove the nuclear cores from all five missiles to stop the launch. She increases her body temperature to the same temperature as the launch chamber to bypass the temperature-sensitive security system of the submarine.
She has only four minutes.
Nadia deals with heat exhaustion, Davik attacks Mason. Carter points out that Mason’s abilities had nothing to do with his memories.
That changes the whole thing.
Instincts take over for Mason as he thinks of his family. He defeats Davik just as Nadia takes out the last core. Mason drags her out of the launch chamber and gives her an injection to stabilize her body temperature.
They narrowly escape, boarding the plane as Russian bombers are closing in.
Do They Save Asha?
The team prepares for an exchange with the nuclear cores on the way to Valencia.
Mason and Nadia run into Christoph while Carter sets up a sniper’s nest nearby. Asha is held hostage on an overpass above them.
The cores have arrived, but Christoph’s men find that they are encoded. Tension is rising. Nadia signals Carter.
He shoots.
The man with Asha gets hit and falls but Mason lunges forward and catches her just in time. Christoph gets away with nothing but Nadia takes care of the rest of the threats.
Mom and daughter are reunited at last.
Who Betrayed Citadel?
The agents arrive at the Citadel headquarters to find the facility destroyed. Mason catches up again with Abby, Hendrix, Carter and Nadia.
Carter says he has figured out a way to give Mason back his lost memories. Abby hesitates, but Mason agrees.
And once injected, everything rushes back.
The truth is crushing.
Flashbacks show that Mason had secretly met with Dahlia years ago.
Then the biggest twist of the season comes:
Dahlia is Mason’s mom.
She survived the explosion in Serbia, after many skin grafts and never went home. Dahlia says Citadel bombed innocent civilians after a mission went bad.
She persuaded Mason to give her classified agent information, believing that Citadel needed to be exposed.
It was that betrayal that brought down Citadel.
By the end of the episode Mason has his memories back, Abby wonders what he remembers, and Nadia watches in silence, knowing things will never be the same again.
Episode Recap
The biggest revelations of the season come in episode 6, but it still has the slick, action-packed style that the show is known for.
The submersible mission offers some tense moments, but never reaches the emotional or narrative depth it aims for. The best part of the finale is the twist with Dahlia and Mason. This brings in some moral ambiguity and gives the story some real emotional weight.
The Serbia backstory is especially compelling, and gives us a glimpse of the gray areas the series has teased all season.
Some plotlines are still a little shallow, but it does leave some interesting questions for the future in the finale. Now that Mason’s betrayal has been revealed, Dahlia’s true identity has been revealed and Abby is now fully involved, Season 2 has a lot of potential.
