Hunting the Hunter

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

Walkthrough
Once the Sole Survivor has been welcomed to Acadia, talking to Dejen on the first sublevel will eventually bring up the topic of an Institute Courser presence on the Island. Dejen claims the courser tracked Chase all the way from the Commonwealth because she "screwed up" during her last visit there, and he tasks the Survivor with hunting down and eliminating the threat to Acadia. The target can be found at a radiant location somewhere on the Island. Once the courser lies dead, returning to Dejen ends the quest with a reward in caps.

Bugs
After killing the Institute Courser, the Sole Survivor could be unable to speak to other NPCs, starting line being constantly "Hey, Dejen". To fix this, just end the quest by speaking to Dejen again.