Far Harbor ( add - on ) Far Harbor is the third add - on for " Fallout 4 " , the second add - on that includes quests and a main story , and was released on May 19th , 2016 . Plot . The add - on is set on the island of Mount Desert Island , off the coast of Maine . There , the Sole Survivor will search for a young woman and a colony of synths . This leads to the fighting between the Far Harbor citizens and the Children of Atom , but a greater plot involves a synth , who has ties with Nick Valentine . The add - on starts off when the player character listens to a radio message from the Valentine Detective Agency after completing the quest Getting a Clue , or when the player goes to the Nakano residence ( possibly even before meeting Nick Valentine ) . Arriving at the office , Ellie Perkins will tell Nick and the Sole Survivor to investigate the case of Kasumi Nakano - the missing daughter of a fisherman living beyond the northeast boundaries of the Commonwealth . A brief investigation at the Nakano residence will tell the player that Kasumi believes herself to be a synth replacement , and that she ' s decided to leave her parents and travel to a place far north called Far Harbor to be with people like her . Traveling to Far Harbor , the Sole Survivor learns that on the island , there are three factions that have been in tense dispute with each other ; Far Harbor ' s citizens , the Church of the Children of Atom , and Acadia , a place specially set up as a synth refuge . The reason for the tension is the radiated fog that has been slowly overcoming the island ; the people of Far Harbor cannot live with the fog and they use machines called Fog condenser s to create fresh air , an act viewed as sacrilege by the Children of Atom who worship radiation and consider the fog the will of Atom to make the whole island a holy place . Stuck between the two sides is Acadia , which only wants peace and harmony . The leader of Acadia , a synth named DiMA , provides the townspeople with the Fog Condensers while at the same time giving the Children of Atom their own base , a former submarine base called The Nucleus for them to live in . But as tensions rise , Acadia is under pressure from both factions to take a side and help eradicate the other . Upon reaching Acadia , it is revealed that DiMA is a unique model synth like Nick , and calls him a " brother . " DiMA explains that he couldn ' t bear seeing Nick going through all the cruel experiments in the lab and so , about a century earlier , DiMA made an escape with Nick from the Institute . However once outside , Nick started to panic and attacked DiMA as he was still under the effects of the experiments , forcing DiMA to " knock the daylights " out of Nick and then leave him to his fate . When the two meet again , DiMA is very pleased to be reunited with his brother , though the case does not appear to be so with Nick . Back to the present , DiMA shows no hostility towards the Sole Survivor , expressing that everyone is welcome at Acadia and that he hopes to find a solution to the dispute without any bloodshed . To do that , he needs to retrieve his early memories of the island that have been locked away at the Children of Atom base . The raw capacity of his model does not allow him to store a large amount of memories . Since the Sole Survivor is unknown on the island , DiMA entrusts the task to the player character . Successfully taking back the memories , the Sole Survivor learns that DiMA himself , though he initially appears friendly and keeps the peoples interest at best , has some deep - buried secrets related to the conflict on the island . Before he set up Acadia , tensions between Far Harbor and synths were high . DiMA , desperate to find a way for his people , decided to kill Captain Avery and replace her with a synth - something he shows great remorse and guilt about - so he can have a " moderate voice " able to calm the residents of Far Harbor . Second , he devised a contingency plan to shut down the power source of Far Harbor which would effectively kill all of its residents . Lastly , he possesses the detonation key of the submarine ' s nuclear missile that , if activated , will destroy the Children of Atom base . All three of the pieces of memory are locked away from DiMA himself , as he can bear neither the thought of mass killing , nor the guilt over the murder he committed . From here the player character will get the option to decide the fate of Acadia and subsequently the fate of the island as well . The player can destroy either the Far Harbor town , destroy the Children of Atom , or if they have sided with either of the three main - game factions , have the Institute reclaim all the synths or have the Brotherhood annihilate Acadia . The player can also forge a peace between all three factions by forgiving DiMA and supplanting High Confessor Tektus with a synth replacement , effectively pacifying the Children of Atom . Supply routes can be established and people moved between the settlements on the two regions .