Mary arrives in France to formalize her arranged marriage to Prince Francis, but complications arise when she meets his attractive half brother and skeptical mother in the series premiere of this historical drama about young monarchs.

Mary and Francis play up their romance after an English envoy expresses doubts about their union. Elsewhere, Catherine seeks to eliminate an individual who's aware of her scheme to destroy Mary.

Mary and Bass return to the castle, where Catherine remains resolved to keep Francis safe from Mary. Meanwhile, Francis learns of the dark prophecy, but it does not dissuade his desire to marry Mary.

Mary's brother visits and asks her to return to Scotland, but Francis is suspicious of his motives. Meanwhile, Penelope takes command as Henry's mental instability progresses; and Lola is skeptical about Julien's marriage proposal.

Mary's uncle arrives at the castle and brings dire news about her mother, forcing Mary and Francis to make a tough choice about priorities. Meanwhile, Henry devises a destructive plan; and Bash and Kenna grow closer as they strengthen their forced union.