Here's the synopsis courtesy of Wikipedia:
It's been over 300 years since the Salem witch trials. Those who remain are almost extinct and in danger again. A school has opened in New Orleans to teach protection to the young. The long-absent Supreme arrives to also protect the new students and their secrets. The themes include witches, witch hunts, incest, minorities, slavery, mothers and daughters, and witchcraft versus voodoo. This season will be set in modern day and the 1830s.
American Horror Story: Coven stars Jessica Lange, Lily Rabe, Evan Peters, Sarah Paulson, Kathy Bates and Angela Bassett. You can catch it on FX October 9th.