On Fortune's Wheel is an adventure story told in three parts. In Part One Birle is "The Innkeeper's Daughter."

But she is not content to spend her life working from dawn till dusk, baking bread, scrubbing floors, or attending to the many other duties of the inn under the direction of her stepmother. So, when she has a chance for adventure, she takes it willingly and begins a journey down the river with Orien, a young Lord, who, like Birle, is unhappy with his fate. Their journey, however, ends in shipwreck, and they are sold as slaves in a foreign land.

In Part Two Birle becomes "The Philosopher's Amanuensis." Her master is a learned man who appreciates the fact that Birle can read and write. She becomes his secretary, recording his notes and observations on the healing power of plants. But when war breaks out, Birle and Orien escape and begin the long journey north, back to their homes.

In Part Three Birle is "The Earl's Lady." Although Birle and Orien are married and she is expecting their child, she is not content with her life at court. She returns to the house and land once held by her grandparents.

But Orien, too, forsakes his role as Earl, and is reunited with Birle and their child as they once again begin a new life together.

Although the plot follows the traditional pattern of a hero tale, the focus is on the heroine. As fortune's wheel forces Birle to face hardships and dangers, she meets each encounter with courage and intelligence.