This is a story achievement obtained during chapter 1, if you choose to play as Emily.
*** Spoiler - click to reveal ***After escaping from your chambers and making your way to the throne room, you get the objective to eliminate the douche who took your ring. When you pickpocket him or loot his body, you take the ring and unlock the achievement.
Given the 100% unlock rate, it's safe to assume that you get this achievement playing as Corvo too.