Reign handelt von der jungen Mary Queen of Scots. Bereits als Baby wurde sie nach dem Tod ihres Vaters zur designierten Königin, wegen ihres Alters aber eher Spielball der älteren Politiker denn angehender Souverän. So handelt die Serie davon, wie Mary samt einiger Zofen an den französischen Königshof geschickt wurde, wo sie auf ihre Heirat mit dem dortigen Thronfolger vorbereitet werden soll.

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.

Maria, adolescente regina di Scozia, è mandata in Francia per sposare il futuro re ma deve lottare contro intrighi politici, scandali e pene d'amore.