Talk to Mitch to start this quest, as part of the checklist quest The Changing Tide. He'll ask you to check out his uncle who lives alone. You can either convince his uncle to go back to Far Harbor or at least make sure he's okay.
Head to the National Park’s Visitor Center. Keep an eye out for mines and traps. Head there and talk to Uncle Ken. After talking to him, this location becomes another settlement for you. He’ll tell you that another attack is incoming so build whatever defenses you can from the available materials in the workbench. You can build at least two Heavy MG Turrets. Place them near the two entrances then repel the Trapper Attack. Once done, you can either convince Uncle Ben to go with you back to Far Harbor or let him stay as a settler in this location. Return to Mitch to report the progress of your quest. If you let Uncle Ken stay behind, Mitch will convince some locals to live in the settlement.