Betray your friends in the Gallows Brothers quest.
To unlock this achievement you must ensure that Henry betrays his friends, Matthew and Fritz, during the 'Gallows Brothers' side quest. You can find them at the tavern near the Sasau monastery. Complete the chain of quests related to their story until you reach the point where they want to steal from the Talmberg quarry. At this point you should refuse to help them, inform Sir Robard and watch them fail. They will then be hanged a few days later, triggering the achievement.