Some Vatican inquisitors punish those believed to be a Protestant. Lord Condé ends up being abducted.

Mary's mother (guest star Amy Brenneman) returns to advise Mary that her throne is in jeopardy. Mary makes a shocking proposition to Conde, along with a bold move to reclaim her throne. Francis moves closer to Lola after a setback with Mary, while King Antoine (guest star Ben Aldridge) makes Kenna an interesting offer. Megan Follows, Craig Parker, Rose Williams, Celina Sinden, Torrance Coombs and Jonathan Keltz also star.

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.

Charles' coronation nears, forcing Mary to find a suitor who will be her ally. Meanwhile, Lola discovers who's been poisoning Elizabeth; and the castle's serial killer has special plans for Catherine.

Gideon shows Mary what life could be like if she chose love over country. Catherine fights to cover King Charles' increasingly erratic behavior, while Claude finds an enemy in her sister Leeza.

Mary’s life hangs in the balance — Childbirth threatens to take Mary’s life, which leaves her and her unborn child’s safety in jeopardy. Elizabeth discovers that someone in her inner circle was the cause of the death of someone close to her.