Sheriff Holston Becker and his wife Allison receive permission to have a child within the Silo, an underground bunker housing the last of humanity. But Allison's doubts draw them both into a larger conspiracy about the Silo's existence and why the human race cannot go outside.
Holston visits a mechanic named Juliette after she claims that her lover, George Wilkins, did not commit suicide but was murdered. As the sheriff considers the case's unsettling connection to his wife, Juliette steels herself to discover what George had learned prior to his death.
Mayor Jahns and Deputy Marnes make the long trek to the bottom of the Silo to meet Juliette, who Sheriff Holston surprisingly recommended as his replacement. But she won't leave until the reactor has been repaired – forcing a dangerous task that plunges the entire Silo into darkness.
Convinced that the mayor was murdered, a despondent Deputy Marnes asks for the new sheriff's help in proving it – though she clearly comes to the upper levels with an agenda of her own.
Juliette is forced to take on Paul Billings as her new deputy, but continues her investigation into George's death despite his clear connection to Judicial. Robert Sims takes action to maintain order within the Silo.
Juliette uses one of George's relics to incriminate Doug Trumbell, hoping to convince Judicial to allow her to open a wider investigation into the possession of illegal relics within the Silo. When Juliette and Paul argue, she reveals that she knows the secret he is hiding even from Judicial.
After discovering that the woman who holds answers has been drugged in long-term medical care, Juliette turns to Judge Meadows – and then pressures her estranged father to help her get her out.
Juliette recalls what her mother did to run afoul of Judicial many years ago. In the present, she searches for someone who can help her gain access to the hard drive.
As Sims and his agents lead a manhunt for Juliette, she seeks refuge in the one place she believes he will not look. Meanwhile Deputy Billings decides to take the investigation into his former boss into his own hands.
Backed into a corner by Bernard and his desire to preserve order in the Silo, Juliette must make a fateful decision to protect the people she loves – and to finally get the answers she is after.
