Hidden between the lines of the history books is the story of Mary Stuart, the young woman the world would come to know as Mary, Queen of Scots. The teenage Mary is already a headstrong monarch - beautiful, passionate and poised at the very beginning of her tumultuous rise to power. Arriving in France with four close friends as her ladies-in-waiting, Mary has been sent to secure Scotland's strategic alliance by formalizing her arranged engagement to the French king's dashing son, Prince Francis. But the match isn't signed and sealed, it depends more on politics, religion and secret agendas than affairs of the heart. Prince Francis is intrigued by the fiery Scot, but like most young men, he resists the idea of settling down into marriage, especially when he has a history with a lady of the court and his own point of view on the wisdom of an alliance with Scotland. Still, an attraction between Mary and Francis is ignited.

The second season of Reign begins with Mary and Francis on the throne of a nation burning. France is rocked by the aftereffects of the plague, a disease that creeps inside the castle walls, taking thousands upon thousands of lives across the land, and ravages the stability of a nation. From the ashes, powerful lords will rise, carrying out personal, religious and political vendettas, taking lives, and tearing at Mary and Francis's commitment to each other, and their people. Friendships will be tested, loved ones murdered and betrayed. Meanwhile, a mysterious and deadly threat snatches victims from village streets and castle corridors; leaving evidence of savagery that looks like the work of monsters; mythical creatures who are the subject of nightmares, but who walk among us, doing the Devil's bidding.

Reign begins its third season with Mary and Francis realizing that they are more powerful together than apart, believing there is hope for them to move forward, leaving behind the anger and hurt. It also introduces us to another Court, that of Elizabeth, "Virgin" Queen of England. Still early in her reign, Elizabeth faces opposition on all sides, particularly from men who doubt a woman's ability to rule. Like Mary, and Catherine de Medici, she struggles to hold onto power, and love; the women have much in common, and Mary and Elizabeth are reluctant foes, but foes nonetheless, each positioned by birth and fate to destroy all the other holds dear.

Reign begins its fourth season with Mary vowing to avenge the death of a close friend. Power struggles continue as the beautiful, passionate and poised Queen continues her journey.