It's a French series about a young woman who has been writing successful horror novels with the inspiration of her recurring nightmares about a witch, Marianne. When she decides to stop writing about her after 15 years, her nightmares return with a vengeance, seemingly intersecting with her real life, thus forcing her to return to her hometown to find out what is happening.
I know, doesn't really sound like anything new, but I'm 4 episodes in and very pleasantly surprised. There are some wonderfully eerie scenes that truly manage to build suspense. Without spoiling anything, there is also an actress who is very, very good at being the creepy grandma of nightmares.