Far From Home

Far From Home is a main quest and achievement/trophy in the Fallout 4 add-on Far Harbor.

Detailed walkthrough
The quest can be started in either of two ways:
 * Find the Nakano residence (north of the coastal cottage in the north east corner of the map) through exploring.
 * After completing Getting a Clue, a new radio station will appear on the Pip-Boy, Valentine's Detective Agency. It has a message from Ellie Perkins to come and see her about a new case. Upon reaching the agency Ellie informs the Sole Survivor of a new client, Kenji Nakano. The man's seemingly uneasy attitude points to the likelihood of a missing person case. Ellie asks the Sole Survivor to meet this new client.

Either way, once at the Nakano residence meet with Kenji and his wife, Rei. They inform the player character that their daughter, Kasumi, has gone missing, and want the Sole Survivor to help find her. Progressive questioning, as well as some Charisma checks, leads the player character to the boathouse, where a holotape can be found locked in an Expert safe. The safe can be unlocked with a key hidden inside a picture frame on a desk. This holotape reveals that Kasumi made contact with a colony of synths near a northern location called Far Harbor. Their presence made her question her own humanity, causing her to run away in order to discover the truth.

Return to the Nakanos and inform them of the discovery. Board the boat to Far Harbor, awarding the Far From Home achievement on the spot.

The miscellaneous missions given after listening to Kasumi's final holotape and talking to Kenji lead to the following quests for the main three factions:
 * Forbidden Knowledge for the Institute.
 * Search and Destroy for the Brotherhood of Steel.
 * Informing Boxer of the Railroad about Acadia. This doesn't lead to anything specific except Boxer moving to Acadia under the pretense of starting an alliance between the Railroad and Acadia.