Cloudy With A Chance Of Fog

PREMISE: During a period of intense storms and cold weather, a thick fog blankets the land.  People report seeing shapes in the fog, especially when alone in the woods.  Soon, people start dying of fright and freak hunting accidents.  When the player's Adepts venture forth into the woods to investigate, they quickly discover that the fog is in fact a massive spell cast by a witch to show people their worst fears.
THEME: This is pure horror-movie style storytelling. The Adepts must venture into the mysterious, dark woods to quite literally confront their worst fears. No matter how horrible you make it sound, it will matter little if the players don't properly role-play the emotional fright and turmoil their Adepts must wrestle with while confronting these horrors. If the players refuse to go along with the theme and treat the mysterious fog like a cheap parlor trick, feel free to punish them by informing them their character just lost all willpower and went catatonic, or they went crazy from confronting their inner-demons and are now running wildly through the woods!
CRISES: A powerful and angry Witch has put a curse on the land. Stopping the curse means getting to the Witch to break her magical objects which she used to cast it (like her book of spells, or whatever serves as the Witch's source of magick). But to do that, the Adepts must get through the fog first...
Remember that, before the Adepts can find the Witch, they first have to work out where she is in the fog. Presumably the fog is covering "the land" which is often a sizable patch of square miles. The players, if they are smart or clever, will do some historical digging first to uncover any local legends of witches cursing whole towns with fog and whatnot. Of you could toss them a bone in the form of a vision, realization or prophecy. It's up to you.
Facing their enemies in the fog wont be about martial prowess. The enemy exists inside their heads, after all. Instead of rolling attributes like Strength, the players will more often find themselves rolling things like Willpower and Courage and Faith. The illusions will appear to take solid forms, and player's Adepts can do things like dodge or parry and whatnot, but in the end these things exist more inside them than outside them.
RESOLUTION: This type of story is meant for character development. If someone's been wrestling with past issues, especially secret issues, now is the time to force the player to confront them. Or you could use this session to open up past wounds or secrets. The main point here is that the characters are fighting enemies within, not without. This is a battle of wits and courage, not muscle, bone and supernatural might.