I loved the teaser, but disappointed we didn't get to see Emma nor Gabby makes me think they won't be main characters and won't be in alll the episodes
Episode 4.01: "Monsters Among Us" Synopsis Revealed
FX have released the synopsis for Episode 1 of the Fourth Season; Freak Show. Written by Ryan Murphy and Brad Falchuk and Directed by Ryan Murphy.
Quote:
“One of the only surviving sideshows in the country struggles to stay in business during the dawning era of television. When police make a terrifying discovery at a local farmhouse, the eccentric purveyor of the freak show sees an opportunity that will lead her troupe either to their salvation or ruin.“
Not OCT 8 
makes me think they won't be main characters and won't be in alll the episodes 
