Mary contemplates how to take over the English throne; Elizabeth struggles to find an appropriate suitor to marry. James gets caught up in a scheme orchestrated by John Knox.

Mary and Darnley are at odds as their plan to seize England is put into action. Elizabeth is conflicted about her feelings for Gideon. Catherine's son Henri tries to claim the throne from Charles.

Darnley teams up with John Knox to strip Mary of her throne, which will leave a close friend of Mary's dead. Elizabeth must banish Gideon from court at the request of her future husband, while Charles takes a bold stance against his brother Henri.

Mary pursues justice by launching a counterattack on her conspirators. Elizabeth suffers a major setback, and it turns her world upside down.

In the series finale, Mary changes the course of history with a decision she makes, and her perilous move for survival causes her to have a stunning realization. Meanwhile, Elizabeth steadies herself for war and becomes the instigator in Mary's demise.