The Arrival

The Arrival is a side quest $$==Quick walkthrough==

Detailed walkthrough
Upon talking to Chase after arriving in Acadia, she tells of a synth runaway who was supposed to have arrived recently but has not shown up. She asks the Sole Survivor to talk to Brooks, the general store trader in Far Harbor, as he is a synth and the person who first meets incoming runaways. She gives his production code to persuade him to help.

Talking to Brooks, he pretends to not know what the Sole Survivor is talking about until telling him his code, at which point he begins cooperating. He explains that the synth came in frightened and ran off before Brooks could tell him where to go. He says the synth ran off to the south of the town.

Going south, follow the marker to a pool of blood and inspect it. Markers will pop up, leading down the road to a house near the shore. There, one will be confronted by trappers. One can either pass a speech check (medium difficulty) and talk to them peacefully, or kill them. If the player character has the Cannibal perk, they may choose a low difficulty speech check instead. When talking peacefully, they say that the synth came by wounded and, not wanting to pass up a meal, they ate him. They give the Sole Survivor his head. Without the speech check, they will become hostile. Kill them and loot the bodies to find the synth head instead.

Return to Chase and she will offer a reward. Three increasingly hard speech checks can be passed to get more caps.