In England, Elizabeth is now being counseled by Catherine de Medici, together they seek Mary's downfall. In France, Francis must deal with his declining health.

As Francis' condition worsens he has plans for Mary's future and the next King of France.

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. 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 gets closer as Mary discovers who poisoned Elizabeth and Catherine becomes a different kind of victim of the castle's killer.

Mary might have to sacrifice her cousin's life to save her own, as she and Gideon find themselves in uncharted emotional territory. Catherine's past returns to haunt her, while Lola and Elizabeth become unlikely allies.

Mary (Adelaide Kane), in order to protect Elizabeth (Rachel Skarsten), unknowingly puts Gideon's (Ben Geurens) life in danger. To save him, Mary turns to another Englishman for help - Robert Dudley (Charlie Carrick). Meanwhile, Bash (Torrance Coombs) is determined to track down the men behind the threats to Catherine (Megan Follows). Anna Popplewell, Craig Parker, Rose Williams, Celina Sinden and Jonathan Keltz also star.

Mary realizes her need to return to Scotland is becoming increasingly imminent and that along with the help of Bash, she must raise her own army to save her throne. Elizabeth enlists Lola's help to find out information about her mother, which backfires when Lola gets caught.

Lola tells Mary she may have a chance to get to Scotland. A murder takes place and Catherine is framed for it. Mary must decide if she should help Catherine or leave for Scotland. If Mary helps Catherine it could eliminate the possibility of safe passage to Scotland. Written by Brittany

When Mary arrives in Scotland, she is stunned by the treacherous world it has become and is forced her to keep her royal identity a secret until she learns who she can trust. When Elizabeth jeopardizes her standing with an unbearable new suitor, Lola steps in to help, which causes the Queen to question Lola's ulterior motives. Meanwhile, Charles secretly plots to relinquish Catherine of her power.

With Mary (Adelaide Kane) presumed dead, Elizabeth (Rachel Skarsten) enlists Lola's (Anna Popplewell) help in taking the Scottish crown for herself, while Mary's half-brother James (guest star Dan Jeannotte) must defend her throne from John Knox (guest star Jonathan Goad). Meanwhile, Mary comes face to face with Francis's killer when she and Bash (Torrance Coombs) find themselves in the hands of a fearsome clan leader named Munro (guest star John Barrowman). Megan Follows, Ben Geurens, Craig Parker, Celina Sinden, Charlie Carrick, Rose Williams and Jonathan Keltz also star.

Mary makes a bold move to defend her reign in Scotland, which results in a battle royale with her cousin, Elizabeth. Lola is accused of a heinous crime and suffers the drastic consequences. Meanwhile, back in France, Catherine finds that Charles has returned a changed man after paying a price for his mother's relentless quest for power.