Duty or Dishonor

Duty or Dishonor is a quest in Fallout 4.

Quick walkthrough

 * 1) Speak to Knight Sergeant Gavil
 * 2) Search for evidence.
 * 3) Read Knight Lucia's log or pass a speech checks with Lucia
 * 4) Talk to Knight Lucia
 * 5) Shadow Initiate Clarke
 * 6) Confront Initiate Clarke
 * 7) (Optional) Exterminate the Ghouls
 * 8) Confront Initiate Clarke
 * 9) Kill Initiate Clarke or convince him to turn himself in or tell him to leave the Brotherhood of Steel (If you choose method 2 or 3, don't kill the locked up Feral Ghouls Below the room.)
 * 10) Report to Lancer Captain Kells

Detailed walkthrough
Shadowing Clarke will lead you to the Boston Airport Ruins. Upon entering the ruins, you are tasked with finding Clarke. Go to the right from the elevators that requires an ID card, open the door and down the stairs and through a tunnel. In a room to the left is the body of Knight Rylan. Further down the tunnel you'll be tasked with the optional quest to exterminate the ghouls. At the end where the tunnel is flooded, go up the ramp and through the stairwell/tunnel until you get to an underground parking garage. Traverse the underground parking garage until you get to a subway tunnel. Take the subway tunnel until you get to the next platform, this will lead you to a luggage terminal.

Upon entering, take the stairs down, follow this tunnel until you get to a room that Clarke is in, that`s above the generator room with a bunch of ghouls. If you open the generator room and kill the ghouls Clarke will automatically become hostile forcing you to kill him. Also if you go into the next room adjacent to the room Clarke is in without talking to him will make him hostile as well.

The ID card is on the desk that has the [expert] terminal. You need this to open the doors and use the elevators.

Convincing Clarke to turn himself in grants a piece of armor upon quest completion (T-60C torso with 10% AP costs in VATS reduced). The optional quest objective of killing the ghouls is also completed by having Clarke turn himself in.

Another option is telling Clarke to leave the Brotherhood of Steel, after which you can either lie to Kells or blame Clarke. Kells will put in doubt your words, but will be convinced after the player character insists on the lie. This option grants 50 bottlecaps and some experience.

Despite the captain stating that a team was sent in to clear out the ghouls, the room at the bottom of the ruins remains closed with ghouls inside if you return after completing the quest. You can enter, kill, and loot to your heart's content after Clarke turns himself in.

Killing Clarke yields no armor or weapon rewards, just 100 caps. Killing Clarke, blaming the missing food on Ferals grants 50 caps.