Mary arrives in France to formalize her arranged marriage to Prince Francis, but complications arise when she meets his attractive half brother and skeptical mother in the series premiere of this historical drama about young monarchs.

Mary and Francis play up their romance after an English envoy expresses doubts about their union. Elsewhere, Catherine seeks to eliminate an individual who's aware of her scheme to destroy Mary.

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.

Mary has a chance to get out of her engagement, but it requires lying and sentencing a man to death. Meanwhile, Francis and Bash suspect that Tomas may be disguising his real motives.

An ex-lover of Francis' arrives and brings danger with her, so an uneasy Mary turns to Bash for comfort. Meanwhile, Queen Catherine persuades Aylee to snoop on Mary; and Bash lands in hot water with heretics, who accuse him of disrupting a sacred ritual.

Francis observes the growing bond between Mary and Bash, so he turns to Olivia. Meanwhile, Catherine wants to ensure that whoever threatened Mary is captured; Bash seeks to repay his debt; and Kenna tells her friends about her affair with Henry.

Mary and Francis are taken hostage when the castle falls under siege, and Catherine makes a shocking suggestion in an effort to save them. Meanwhile, Diane reveals to Bash that she's plotting to have him declared legitimate.

Nostradamus shares with Mary his prophecy about a death, which leads Mary to make a big decision concerning Francis. Meanwhile, Clarissa gets brazen as she pursues her goals; and Kenna tells Catherine about Diane's intentions regarding Bash.

Mary and Bass return to the castle, where Catherine remains resolved to keep Francis safe from Mary. Meanwhile, Francis learns of the dark prophecy, but it does not dissuade his desire to marry Mary.

An assassination attempt is made on Bash's life, and Catherine appears to be responsible for it. Meanwhile, Mary offers assistance to a jailed peasant who has a curious link to Bash; and Lola tries to stop Catherine from meddling with Bash and Mary.

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.

Clarissa kidnaps Henry and Catherine's youngest sons, so Catherine turns to Mary and Bash for help. Elsewhere, Lola tries to assist her brother with a debt, but when she gets in over her head, Francis comes to her aid.

Mary must decide whether to marry Bash or Francis, who returns accompanied by Lola. Meanwhile, Mary's mother visits and pushes her own agenda, and her mere presence in the castle troubles both Henry and Catherine.

Mary's honeymoon ends and she returns to the castle. Meanwhile, Lola displays some odd behavior, which leads to a secret being exposed; Bash finds a bewildered Olivia and asks Nostradamus to assist her; and Henry seeks help from Catherine.

Bash saves Francis' life while they're in the woods exploring the latest ominous threat. Meanwhile, Henry becomes obsessed with a servant who won a contest; Greer is seen kissing a kitchen servant; and Henry forces a new couple into a union.

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's brother visits and asks her to return to Scotland, but Francis is suspicious of his motives. Meanwhile, Penelope takes command as Henry's mental instability progresses; and Lola is skeptical about Julien's marriage proposal.

Mary's uncle arrives at the castle and brings dire news about her mother, forcing Mary and Francis to make a tough choice about priorities. Meanwhile, Henry devises a destructive plan; and Bash and Kenna grow closer as they strengthen their forced union.

Mary hires a mercenary to help her save Scotland. Meanwhile, Francis prepares France to wage war on England, and Leith becomes his ally in this endeavor; and Lola and Julien's bond deepens, but she fears he will betray her.

Mary teams up with Catherine to deal with Henry, whose deranged behavior puts Francis at risk. Elsewhere, Bash resolves to destroy the Darkness after meeting a boy who survived the horror; and a devoted Lola tries to protect Julien.

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.