A Portuguese prince offers much-needed aid to Scotland if Mary accepts his marriage proposal and break things off with Francis. Elsewhere, Francis' feelings for Mary lead him to put Bash in a risky situation.

Henry claims Catherine has committed treason and adultery, so she attempts to save herself by shedding light on a dark part of Bash's past, and Bash and Mary then try to even the score. Meanwhile, Nostradamus discloses the truth about the castle's ghost.

Mary uncovers her marriage contract's secret clause, which was added by Catherine and her mother, so she and Francis attempt to persuade the people of Scotland to renounce her mother.

Mary and Francis take drastic action in response to Henry's madness. Meanwhile, a terror in the woods puts everyone in peril; and Mary makes a bold choice when she discovers Lola is in the midst of a life-threatening labor.