Warhammer 40,000: Dawn of War II

There are two missions on the Space Hulk. The first one is mandatory but the second one is optional. You have 3 days to do the second one after doing the first. In the second you have to recover Galen's log. After the mission the log is in your inventory as an expendable item. When you dispose of it you get message in your mission log and this achievement.

One thing, disposing of the log gives all squads corruption so if you want to be pure and have a redeeming item hold onto it until you get this.