Whether disturbing content is on or off decides when you get this achievement.
On: complete “Davis Family Vacation”.
Off: complete “Mind The Gap”.
*** Spoiler - click to reveal ***Disturbing content: decides whether the mission “Davis Family vacation” is playable. The mission is a short cutscene where the Davis family, consisting of Mr and Mrs Davis and their (4-6 year old?) daughter, are enjoying a walk down the streets of London until they are blown up in a nuclear explosion.