52 was a weekly series that takes place during the missing year between the Infinite Crisis and One Year Later crossover events. It tended to focus on secondary characters as the Trinity, including Wonder Woman, were missing or out of action during this period, and examined a full year in the life of some of these characters before catching up to the regular publications in One Year Later.
One of the key events that forced Diana to withdraw from the world was her slaying of Checkmate’s Black King, Maxwell Lord, in Wonder Woman #219. Max had used his telepathic powers to take control of Superman, turning him into his own personal instrument of destruction. In order to stop him, Wonder Woman had snapped Lord’s neck, killing him. This single act of cold blooded execution earned her great enmity from the super-hero community. So, like Bruce Wayne, Diana decided to retire from her heroic identity and spent the following year coming to terms with her actions. She eventually decided to serve humanity as an espionage agent and Bruce Wayne provided her with the cover identity of Diana Prince working for the Department of Metahuman Affairs.