The Arrival

 is a side quest in the Fallout 4 add-on Far Harbor.

Walkthrough

 * 1) Talk to Chase at Acadia. You'll be asked to bring back a synth that was supposed to arrive.
 * 2) Travel to Far Harbor. Talk to Brooks and give his designation as password. He'll say that the synth arrived prematurely and seemed to be convinced they have a Courser on their tail. He'll tell you to search south.
 * 3) Follow the road south. Look for blood trails. Find the house with trappers inside, at a small dead end on the coast, just east of Acadia.
 * 4) Talk to the trappers. Either kill them or use persuasion to procure the synth's head.
 * 5) With that in tow, head out to Acadia and hand the noggin' to Chase.
 * 6) Mission accomplished.