From Exalted - Unofficial Wiki
A circle of newly exalted Solars is gathered by a Sidereal who calles herself Cassandra. Cassandra is actually the Green Lady. I am not going to reveal her true motives yet , since the Campaign is still in progress. The Circle "finds" a small girl in the woods near their Manse , who is capable of creating and shaping Wyld areas. They soon find out , that the girl is actually a Demon of the Third Circle , the Heart of Oramus (NOT canon). They are send by "Cassandra" to throw her in the Void , since only that could destroy her. The girl "matures" over night during the journey and informs the Circle that this is her true form. The girl was only a way to get used to creation again after 500 years of absence. She reveals Cassandra's true nature and convinces the Circle to head towards Walker's Realm.
The Story is bit more complicated but we are only in the third session.