As Mary and Francis investigate who was behind the poisoning of King Henry (Alan Van Sprang), they unearth secrets of the past which force Mary to confront her feelings for Conde as she attempts to move forward. Catherine finds herself in the middle of a romantic triangle when the Duke of Guise (guest star Gil Darnell) returns, which forces Narcisse (Craig Parker) to commit a hideous act out of desperation. Meanwhile, Greer (Celina Sinden) finds herself in a situation she never fathomed in order to survive.

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.