Instead of doing odd-jobs for the Children of Atom to gain High Confessor Tektus' trust, you could just pass him the launch key and the means to take down Far Harbor's defences - just be sure to tell him you're not ready. (Speaking to DiMA here will cancel the 'An Execution' and 'What Atom Requires' sidequests if not completed.) Fallout 4 Far Harbor DLC: PS4 vs Xbox One Gameplay Frame-Rate Test Once you have everything, leave the hideout and fast travel back to Acadia. Enter Martin's old hideout, pick up the holotapes, grab the mother icon and have a read of the notes lying about.
There's a sewer opening covered by moss that you need to walk through.
When you get to a crashed VIM! Truck, go around the back and wade into the water. Head back out into the wastes and go West to recover Martin's holotapes. It looks like a neck brace, but don't worry about it - Fallout 4 doesn't play great in third-person anyway. Before you leave, DiMA will grant you with Acadia's Shield, a powerful and unique armour piece that grants +1 to agility, intelligence and endurance. The plan is to take the Children of Atom's leader, High Confessor Tektus, and replace him with a replicant that will convince the faction to work towards peace with Far Harbor. If you tell DiMA you will keep his secret, this new branch will open up, revealing the ending with the least bloodshed.