Story-based and cannot be missed. Chronologically comes after "Home Sweet Home" and you unlock
Synopsis:
*** Spoiler - click to reveal ***After returning to Helios, you find that The Lost Legion is blocking your way to where you need to go. Jack devises a plan to involve three scientists to override the barricades. He requests that you go gather them up. As you find each of the scientists, they will have their own needs that you'll need to meet: fetching a picture, retrieving a teddy bear, recovering a lost keycard. You will make your way back to Jack in his office, watch the murder of the scientists you just spent that time saving, and then...
... you get the achievement once you turn it into Jack.