Margery Fitzgerald is a devout Catholic who struggles between her religious convictions and her love for Ned Willard. She plays a significant role in the story's exploration of loyalty and personal beliefs.

Rollo Fitzgerald is the primary antagonist, driven by his strong Catholic beliefs and desire for power. He is in direct opposition to Ned's advocacy for religious tolerance.

Sylvie Palot is a dedicated Protestant and bookseller from France, known for her courage and commitment to spreading the Protestant faith. She forms a significant bond with Ned Willard.

Pierre Aumande is one of the novel’s major antagonists, known for his ambition and manipulation in pursuit of political power. He acts as a spy and is involved in various schemes to further his aims.

Barney Willard is Ned’s adventurous older brother, who becomes an experienced sailor. He plays a key role in the naval aspects of the story and is known for his flirtatious nature.

Ebrima Dabo is a former enslaved man from West Africa who collaborates with the Willards’ Spanish relatives. He embodies themes of identity and freedom in the face of oppression.

Alison McKay is the loyal childhood friend and lady-in-waiting to Mary Stuart. She is skilled in political maneuvering and remains devoted to her queen throughout various challenges.