Once you get to Calvert Mansion, Demond, the ghoul inside the mansion will start ordering you around like he owns the place. Seeing how he's telling you to kill the tribals who are assaulting the mansion and trying to kill you, following his orders and swallowing your pride isn't a bad idea. Better your pride than your spleen.
At this point, simply follow Desmond around killing tribals. Eventually he'll ask you to find out how the tribals are entering the West Wing and to deal with the problem. Make your way through the wing, killing as you go. When you get to a dead end, Desmond will tell you to find a way to seal the nearby hole. Look through the hole to the orange propane canister, shoot it and the explosion will seal the hole. Now you'll have to do the same thing in the East Wing, only you'll take a three story detour via a hole in the floor. Fight your way back up to the top level and make your way through all of the tribals until you get to another dead end and another gas leak. Shoot the canister to seal off that hole and Desmond will open a nearby door.
Follow Desmond to the main area and prepare for the final onslaught. Desmond will tell you to plant any mines you have in front of the boarded up doors, so go ahead and do that. Don't bother putting any mines on the stairs, as the tribals are more than content to just shoot at you from the bottom floor. Desmond will call out where the tribals are coming from so just be alert, use VATS and you should be just fine.
Once everyone is dead talk to Desmond and he'll tell you that he's in Point Lookout on business and that he has no idea why anyone would want him dead. After all, it's not like the mansion is his, he just found it that way. Keep talking to Desmond and he'll make you an offer: go and find out why the tribals are trying to kill you and he'll make you rich. At this point the "The Local Flavor" quest will end, the "Walking with Spirits" quest will begin and you'll get the achievement, 20 points and the "Superior Defender" perk which gives you +5 to damage and +10 to armor when standing still. Not sure if this counts in VATS as you can't fire and run while in VATS, but seriously, running and gunning is so passe. All the cool kids stand rock still and get tore up.
Walking With Spirits - 20 pts
After speaking to Desmond feel free to check his back room for some weapons and ammo. If you're a big fan of energy weapons you won't find much here to satiate you, however the gear is free and given that energy weapon ammo is pretty much nonexistent, some good old fashioned projectile weapons may do the trick. At the very least you can carry them around for spare parts. Once you have what you need, leave the mansion and follow the marker on your map to the Ark & Dove Cathedral. When you arrive at the cathedral use the intercom to tell the cathedral inhabitants that you want to join the tribe. They'll tell you that you need to head west to the Sacred Bog and gather up the seeds of the Mother Punga plant. By the way, Mother Punga is now the best fake swear word I've ever heard.
It wouldn't be Fallout if your missions didn't take you from one end of the map to another and this one ain't no different as the Sacred Bog is as far west as you can go in Point Lookout. Luckily it won't take you long to get there so quit yer complainin' and go west young vault dweller. You'll meet up with various enemies along the way, mostly swampfolk. When you see the small shack start looking on the ground for bear traps. They give no warning before snapping shut on your leg so if you see one, either disarm it with a high enough repair skill or make your way around it. The shack, known as the Tracker's Shack has one of the few workbenches in Point Lookout inside, so if you're in the mood for tinkering, this is a good place to do it. It's also a nice place for a nap should the swampfolk have taken a chunk out of you.
Continue west to the entrance to the Sacred Bog and then head on through the door and then through the next door to the bog proper. The bog is filled with mirelurks, mirelurk hunters and swamplurks (the DLC's version of mirelurk kings) so be on the alert for them as you make your way along the fairly convoluted path. When you get to a clearing bordered by torches, start looking for bear traps again and either disarm them or avoid them.
You'll know the Mother Punga plant when you get to it as it's, well, a giant Punga Plant. Feel free to gather up all of the surrounding wild pungas if you're in need of some radiation relief after your trek through the muck. Once you're ready, approach the plant and activate it to gather up the seeds. The plant will release a cloud of something, you'll fall to the ground and things will start to get weird. Yes, weird even for Fallout.
When you get back up your quest log will tell you to make your way back to the Ark & Dove Cathedral, so start making your way back through the bog to do so. You may notice that the colors are strangely...different. Then you'll see your first bobblehead, a Schmault-Tec bobblehead that essentially makes fun of you. That's just the beginning. Soon you'll be host to all sorts of strange hallucinations including more bobbleheads, Nuka Cola grenades that explode with a baby's whimper and a reunion with dear old mom. You'll also see a strange saw sawing the ground and a needle and thread sewing something back up. Eventually you'll get to Mr. Break standing in front of the bomb from Megaton. Talk to him, the bomb will explode and you'll awaken outside of the entrance to the Sacred Bog.
At this point, if you check your inventory, or go into third person view, you may notice that you don't have any hair, or any headgear and you can't equip any headgear. You also have a scar on your head. Hey, remember when Desmond said something about the tribals cutting holes into their heads and removing parts of their brain? You don't think...nah! That's just silly! I'm sure those hallucinations about saws and sewing were just memories of your home economics and shop classes from the vault. Any way, deal with any nearby enemies and fast travel back to the Ark & Dove Cathedral. Once at the cathedral, use the intercom to gain entrance and then chat with a tribal who will blather on about expanded consciousness, hole in the head, blah, blah, blah. Upon speaking to him you'll finish up the quest, get the achievement and 20 points and get the Punga Power! perk which increases the radiation diminishing effects of Punga fruit. Ending this quest will automatically lead into the next one.
Hearing Voices (no achievement)
No one seems to know where the leader of the tribals is, so look around until you can find Nadine. Nadine will tell you all manner of wonderful things including why they took a piece of your brain out. Ask her if she knows who did it and she'll tell you that she's looking into it and to meet her at the dock in a day or so and she'll have more information. If you speak to her about your scar she'll heal it for you, allowing you to don headgear once again. Incidentally, Nadine is the lost daughter that Catherine has been looking for, so bring up the fact that moms is a'searching for her and she'll say that she doesn't want to go back until she's made a name for herself. Check the Unmarked Quests section of this guide for how to resolve this quest. Eventually Nadine will tell you that she tracked Jackson to the leader's secret cave and lifted a key for accessing said cave. Once you're done speaking to Nadine, your quest will update telling you to go and talk to Desmond. Before doing so find a tribal named Croatoa and talk to him about how he's able to raise such lovely Punga fruit. If you pass a speech check or have the Child at Heart perk he'll give you his special Fertilizer Shovel which causes extra damage per hit. It's not the greatest weapon in the world, but when used in VATS you get to see yourself brain a dude with a shovel. Now that's what I call entertainment!
Once you're done milling about with the tribals, head over to Desmond. He'll yell at you for not investigating the secret leader's cave and tell you to do so. Fast travel to the cathedral and then head to the Sea Tub and enter the cave. Mirelurks of varying types abound so deal with them directly or sneak past them. Eventually you'll get to see the tribals' vaunted leader, a holographic projection of a human brain that goes by the name of Professor Calvert. Calvert will tell you that he had the tribals attack the Calvert mansion because Desmond has a signal jamming device that is keeping Calvert's psychic signal from reaching far and wide. Once the conversation is over, use the nearby ladder to get back to the surface and then head back to Desmond and report your findings. The quest will end and lead right into the next one.