1975’s The Broken Citadel is the first volume in Joyce Ballou Gregorian’s Tredana young-adult portal-fantasy series. The series is Gregorian’s only published fantasy of which I am aware, no doubt because the author died shortly after the third book was published.
Intrigued by the library she glimpses through the windows of a long-empty Victorian mansion, eleven-year-old Sybil “Sibby” Barron breaks into the house. Her visit to the library is a short one. When she exits, intending to rush home, she finds herself on an unfamiliar seashore on another world.
It’s a world rich in ways for naïve young women to die horribly, so it’s all for the best that the first people Sibby meets are Leron, Mara, Gannoc, Dansen, and their guide One-Eye. They are a band of kind-hearted adventurers on a great quest. Sibby joins their party.