Sometime during May 2229, a man by the name of Carter entered Diamond City and joined a group of residents at the bar at the center of the town. Carter started telling stories and making conversation with the people around him. A large group of people started to crowd around him to listen to his stories. After a few hours and having a few drinks, something in Carter shifted. He had suddenly lost his smile and his cheek started to twitch.
Mr. Carter suddenly pulled out a revolver and calmly, without even thinking twice, shot Henry, the bartender, square in the head. Carter continued on his rampage, killing an additional 3 to 4 people before finally being brought down by Diamond City security. Inspection of the corpse revealed that Carter was not an actual human being at all, but was in fact an Institute synth, only more advanced than the previous generations of synths.
This incident came to be known as the Broken Mask incident, and led to the people of the Commonwealth learning of the existence of 3rd generation synths. The Institute paranoia began to rise.
- When inside the Institute, the Sole Survivor may find a holotape recording in Shaun's room labeled as Director's recording 108. After listening to it, it is discovered the synth was a prototype not ready for the field. The synth was sent without the Director's authorization. The Director sounded furious as she goes onto say that there will be a person responsible for the synth in the field and that she will hold them accountable.
- Eustace Hawthorne is the only known resident of Diamond City actually old enough to have witnessed the shooting.
The Broken Mask incident is mentioned only in Fallout 4.