This is a Storyline Achievement! It is unmissable.
The below guide will assume you are progressing from the previous storyline achievement (Reunion)
*** Spoiler - click to reveal ***
Choices from previous chapters will have impacted the general party formation but you will be in a truck on the way to the compound and Luke will be missing.
- Interact with the Butterfly
- Progress through conversation with your party
- Decide if you want to assist Kenny or Not (I did not)
After a few more conversations you will unlock this achievement