Elizabeth must deal with the political backlash of harboring Catherine in England, while Catherine is imprisoned upon her return to France. Mary is forced to make some difficult decisions about securing Scotland's future and Lola is conflicted in her feelings for Narciss.
When King Antoine unexpectedly returns to Court, Mary must help Francis hide his weakening condition long enough to secure his family's future. With the Throne in jeopardy and time running out, they must turn to an unlikely ally in need of redemption.
After Mary receives an urgent message from her ailing mother about the dire situation in Scotland, she finds herself looking to Francis for aid. Catherine finds herself up against Narcisse as she fights to become the regent to Charles. Meanwhile, Elizabeth faces continued pressure to wed.
Grateful for a future with a revived Francis, Mary considers signing away her claim to the English throne, and staying in France forever. Catherine learns that Nostradamus has returned -- with a new vision involving Francis' fate.
Mary realizes she must help Catherine in her quest to become regent, even at the risk of hurting the alliance with Scotland. Claude is determined to help Leith marry while Elizabeth struggles with the prospect of losing Dudley.
When Prince Don Carlos of Spain visits France, Mary uncovers a dark secret he is hiding and enlists in Catherine to advise her on how to handle. When Gideon, the new ambassador from English court arrives, suspicions arise about what his true intentions are, while Bash's pursuit of the mysterious killer comes to a head at Greer's tavern.
As Mary and Catherine deal with the aftermath of Prince Don Carlos' accident, Mary realizes that she will have to marry for the good of her country and not follow her heart. When Catherine is accused of poisoning Francis, Lola is shocked when Mary thinks Narcisse framed Catherine in order to become Regent of France.
Mary becomes suspicious of Prince Don Carlos' true condition and relies on Gideon to help her uncover the truth. Elizabeth makes a shocking discovery which could change the course of her reign over England and forces Dudley to make a tough decision. Meanwhile, Narcisse forces Claude to marry someone of his choosing, against her wishes.
Mary struggles to resist her feelings for Gideon as she works to align herself politically with potential allies. Elizabeth and Greer find themselves in similar heart-wrenching situations with the potential for very different outcomes. Catherine and Narcisse continue their vicious power struggle over the Regency, while Claude finds herself in the fight of her life on her wedding night.
Charles' coronation is just around the corner and Mary looks to align with a strong suitor.
Whilst trying to protect Elizabeth, Mary puts Gideon's life in danger. Bash is determined to discover the men who are threatening Catherine.
Mary has to return to Scotland and raise an army to try and save her throne.
Mary is offered an opportunity for safe passage to Scotland if she moves quickly. Catherine is framed for murder.
Having returned to Scotland, Mary is stunned by the treacherous world it has become.