From Fate/Grand Order Wiki
Heresy of Salem is the setting of Chapter 4 of the main story. It is the 4th Epic of Remnant Episode.
It is indicated that it will happen in a provincial city in the east coast of the United States
It is also indicated that the story will happen during seven days, having a direct impact on the game. Story will be time-locked and chapters will unlock periodically.
Unlock Requirements : Clear Solomon Chapter
Heresy of Salem Chapter will be released on the 29th of November, 2017
Bond Level Bonus
Every Caster Servant will receive double the amount of bond points when playing the main quest
New Servant Class: Foreigner
The Foreigner class debuted in the Salem Singularity. This class is strong against Berserkers, Foreigners and weak to Alter-Egos.