Vault 33 dweller Lucy MacLean volunteers for an arranged marriage with a dweller from Vault 32, which is connected to 33 along with Vault 31, but things go wrong and her father is taken by raiders. In defiance of Vault regulations, Lucy decides to go to the surface by herself to search for her father. Meanwhile, Brotherhood of Steel aspirant Maximus is promoted to the rank of squire and joins Knight Titus in hunting for a member of the Enclave. Elsewhere The Ghoul is searching for the same target, and sets out to pursue the bounty.

Maximus commandeers the armor of a fallen knight. Lucy's quest leads to encounters with Wilzig and a trip to Filly, where she meets The Ghoul.

When Wilzig's head is snatched by a monster, Lucy and The Ghoul try to retrieve it. Meanwhile, Thaddeus unknowingly teams up with Maximus, and dynamics shift in Vault 33.

Lucy and The Ghoul encounter dangerous situations, leading to a moral dilemma and intense confrontations. Norm uncovers secrets in Vault 32, linking back to his mother's past and raising questions about the residents' fate.

Lucy joins forces with Maximus to find Thaddeus, who absconded with the head. Meanwhile, Betty becomes the overseer of Vault 33 and reassigns part of the population to Vault 32.

Lucy and Maximus learn about Vault's 4 refugee policy and uncover unsettling secrets. Meanwhile, the Ghoul has flashbacks to his former life, where he learned of his wife's role in a Vault-Tec conspiracy.

Residents of Vault 4 prepare to expel Lucy for breaching the forbidden Level 12; Thaddeus finds a means to heal his foot; Norm infiltrates Vault 31; Moldaver convinces Howard to distrust his wife.

Norm becomes trapped in Vault 31. Lucy learns the truth of the Great War, and her fathers part in it and other events. The Ghoul, believing his family might still be alive, invites Lucy to travel with him and Dogmeat to find Vault-Tec's leaders. Hank flees to the remains of New Vegas.