Vault 81 (quest)

Vault 81 is a side quest in Fallout 4.

Detailed walkthrough
When the Sole Survivor arrives at Vault 81, proceed to connect their Pip-Boy to the entrance button in an attempt to open the Vault doors; however, the door will not open and instead Scott Edwards will respond to the activation attempt through the intercom system. Overseer Gwen McNamara will dismiss him and take over the conversation.

McNamara will advise the player character that if they want to enter the Vault, they need to bring three fusion cores as a means of payment. Alternatively, the Survivor may pass a Hard speech check. If the choice is made to part with the cores, they will be compensated with 100 bottlecaps by the overseer. Full access to the Vault will be granted regardless. Overseer McNamara will welcome them and they may trade and interact with the residents of Vault 81.

Bugs

 * When you pass the persuasion check there is a chance that the door used to head deeper into the Vault will not open and remain inaccessible. There is no currently found fix for the issue.
 * When you enter the Vault, McNamara will finish her conversation with Calvin and then just look at you. If you try to interact with her she will just stare at you. Saving and reloading the game does not appear to solve this issue. It may be caused by dropping your cores after entering the Vault but before talking to McNamara; picking them up again resolves the issue in this case.