After helping the various vault inhabitants, leaving the vault, and then returning a short time later, the Sole Survivor will be met with a scene of chaos, as the vault residents are in a state of panic over the young Austin having fallen deathly ill due to being bitten by an unknown variant of molerat.
Speaking with Doctor Forsythe and Bobby DeLuca at the vault's clinic, will reveal that Bobby knows of a secret area of the vault where he hid his stash of chems, which is where the molerat had come from. Forsythe will request for the Sole Survivor to search this section of the vault, in hopes of finding an antidote, in which Bobby will escort them to the secret area's hidden entrance.
After reaching the secret section of the vault, and after Bobby leaves the Sole Survivor's party, the Sole Survivor will need to fight through the nesting molerats, and eventually their broodmother, effectively putting an end to one of Vault-Tec's vault experiments, which is revealed to have been the infecting of vault dwellers with various sicknesses, in order to devise a serum that could combat all human illnesses.
The Sole Survivor will then discover the last remaining scientist of Vault 81, a unique Mr. Handy model programmed with a French female personality. After releasing Curie from her containment, she will give the Sole Survivor the last remaining cure, in which the party will then need to travel back to the vault's clinic in order to cure Austin.
Should the cure be handed over, the Sole Survivor will suffer a permanent -10 to the health pool; however, this will gain access to a unique weapon and living quarters in exchange for this sacrifice.
Should the cure be kept or shared, Austin will die, and the Sole Survivor will recover from the health penalty, at the cost of the before mentioned rewards.
Regardless of how the Sole Survivor deals with Austin, this quest will conclude, and Curie will offer herself as a permanent companion option.
In the contained room where Curie is stationed, the Sole Survivor will find the Medicine Bobblehead
Numerous details are spread throughout the secret area of the vault describing the cure's creation. In particular, why it was worthwhile violating ethics to infect Vault 81 because the needs of the many outweigh the needs of the few. However, no moral choice is laid upon the player to decide whether to cure all disease or just Austin, instead only offering the player the cure for the Vault 81 Molerat Disease.
It is difficult, though possible, to complete the quest without contracting the disease. However, if the player character, a companion, or even a protection is bitten, the Sole Survivor will become infected.
The console can be used to spawn a second cure with the command "player.additem 55f10".
As of 2015-12-29, quickly dropping the cure before it is removed after agreeing to save Austin allows the player to keep the cure and save Austin.
(Patched) If the Sole Survivor says to Forsythe that they are keeping the cure, he will ask of them if they really and truly intend to, in which the Sole Survivor will then turn away, and can then use the cure on themselves at their own personal leisure, in order to remove the molerat disease debuff if needed. They can then turn back to the doctor afterwards and say "You are right," in which both the Sole Survivor and Austin will be inexplicably cured.
Occasionally, the infirmary will have two chairs near the table to the left of the entrance, and Dr. Forsythe will sit in one of them. If the cure is handed over to Forsythe while he is sitting down, he will not walk over and administer the cure to Austin. This can sometimes be fixed by exiting vault 81, or by reloading a save.