The cave, named Charleston Cave, is clearly marked on your map, but you can't take a straight northerly route there. Once you've acquired Lily, it's time to find an entrance to the cave in question. A good combination of followers to bring with you for the duration of this side quest is Lily and Rex, since they both specialize in melee, close-quarters combat. You can find her outside just follow your compass instructions. You'll need to clear space for her in your group of followers (if you have two with you, that is). Be sure to take him up on his optional request, too, to bring the Nightkin named Lily there with you. Henry requests that you go to the cave to investigate things there, and you should oblige. Henry wants to get to the bottom of what's going on with the Nightkin, and he suspects that the source of the sickness - and more importantly, the solution therein - rests with the Nightstalker population that inhabits a cave to the north of town. The chronic use of Stealth Boys by the Nightkin community has created a sort of sickness that's endemic with most of their kind. Henry about all sorts of issues, but ultimately, you'll find out that he's here working on the solution to a problem that's been plaguing the residents of Jacobstown, and indeed Super Mutants and (especially) Nightkin around the Wasteland. Henry and his lab assistant, a Ghoul named Calamity.

Within, head right on the first floor to find the town's only non-Super Mutant/Nightkin residents, a human named Dr. But once you do, head forward through the settlement towards the gigantic building towards the back. Getting to Jacobstown is actually fairly annoying, since you'll have to follow a wandering road through the mountains in order to reach it. Jacobstown is a bit of an anomaly in the Mojave Wasteland, since it's a town run and occupied almost entirely by Super Mutants and Nightkin. At the far western reaches of the map, there's a settlement called Jacobstown.

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