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 condensers 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.

Factions

 * Church of the Children of Atom
 * Acadia
 * Trappers
 * Harbormen

Robots and computers

 * Defense construct
 * Indexer
 * Sentry intrusion countermeasure

Settlements
Supply routes can be established and people moved between the settlements on the two regions.
 * Longfellow's cabin
 * Dalton farm
 * Echo Lake Lumber
 * National Park Visitor's Center

Ammunition

 * .45-70
 * Harpoon
 * Modified bowling ball

Weapon effects

 * Blazing - Blocking has a 25% chance to set attackers on fire for 50 damage.
 * Charged - 10% chance to deal 100 Electrical damage on a successful block.
 * Deadeye - Slows time when aiming down sights.
 * Defiant - The final shot in the magazine deals twice the normal damage.
 * Frigid - 20% chance to freeze the enemy when the player blocks their attack.
 * Hitman's - 10% bonus damage when aiming down sights.
 * Resilient - +150 damage resistance while reloading.
 * Resolute - Time slows down for a moment when the final round is chambered.
 * Steadfast - +50 damage resistance while aiming.

Armor effects

 * Auto Stim - Automatically use a stimpak when hit while health is 25% or less, once every 60 seconds.
 * Cloaking - Being hit in melee generates a Stealth Field once per 60 seconds.
 * Cryogenic - 10% chance to freeze melee attackers, once every 20 seconds.
 * Rad Powered - Grants additional strength the higher the Sole Survivor's rads.
 * Unyielding - +3 to all stats when the player is at 25% or less health.

Official trailers
Far Harbor (Add-On) Far Harbor (DLC) Far Harbor (add-on) Far Harbor Far Harbor Far Harbor