Broken Mask incident

The Broken Mask incident took place in Diamond City at the Power Noodles bar in the year 2229.

Event
According to Eustace Hawthorne, a witness of the event, a man named Carter entered Diamond City and joined a group of residents at the town's central bar during May of 2229. Claiming to be from "out west somewhere," Carter made conversation and told stories about the state of the Commonwealth, drawing a crowd of locals. After about three hours and seeming "a bit drunk" from having about four to five drinks, Carter's smile suddenly fled.

As his cheek began to twitch, Mr. Carter unexpectedly pulled out his revolver and, without emotion or hesitation, shot the bartender, Henry, straight in the head. With his cheek still twitching, Carter continued to execute another three to four individuals. As the city guards arrived and opened fire, Carter continued his frenzy, "tossing people left and right." He was eventually "put down" and stopped by security.

Inspection of the corpse revealed chunks of plastic and metal, proving Carter to not be human but instead an advanced synth created by the Institute.

The residents of Diamond City speculated on the reason for Mr. Carter's killing spree, amounting it to either a malfunction or a combat test devised by the Institute. Meanwhile, the Director of the Institute was furious; Carter had been not approved for field testing and was sent to the surface without authorization. As the incident threatened decades of work to keep the organization "out of the spotlight" in the Commonwealth, the Director aspired to identify those responsible.

Aftermath
The lasting impact of the incident is still seen in 2287, generations after the event, in both Diamond City and the greater Boston Commonwealth. The fear of neighbors and family members unknowingly being synths steadily developed, growing into widespread paranoia and mass hysteria.

Appearances
The Broken Mask incident is mentioned only in Fallout 4.