This a story related achievement and should be unmissable.
Near the start of the episode you will experience your first flashback/memory and opening credits. Afterwards you will have a very short conversation with Mantis at the bar in Nowhere. Once this conversation is over you should see the achievement pop.
If you go through the next part of the story
and it doesn't pop then quit out of the game at the dashboard then when you load it up again restart the episode. There is a bug which stops achievements popping during this episode and it happened to me twice, this was the only solution that worked for me.