Find the missing people for Marcus

Go see Marcus, the mutant town sheriff, and ask him to do this quest.

Afterwords, locate a man named Dan in a house in the north-east corner of Broken Hills. He will tell you that his wife is missing, and you will be able to find her and get some XP.

Being in the east side of town, find a manhole (there's one in an outhouse), there are a few in that area.

You will have to face a few giant ants, but they're probably nothing you can't take on by now. Then in the tunnel, locate the mass amount of dead bodies, and find the body of a woman (more precisely, Dan's wife). There will be a note on her body.

The note implies that Francis is the killer of these missing people.

Go back to Dan, and tell him you found his missing wife... er, dead. You will receive 500 XP for this. Then talk to Marcus to get more. If you refuse money, you receive from him Scoped Hunting Rifle.

Also, if you have defeated Francis in arm-wrestling, you can confront him with the note you found (yay, more XP) and then he will leave the town.