Queen of France at sixteen, widowed at eighteen, Mary Stuart defies pressure to remarry and instead returns to her native Scotland to reclaim her rightful throne. By birth, she also has a rival claim to the throne of Elizabeth I, who rules as the Queen of England. Mary asserts her claim to the English throne, threatening Elizabeth's sovereignty. Betrayal, rebellion, and conspiracies within each court imperil both Queens, driving them apart, as each woman experiences the bitter cost of power.