Charles learns of Catherine and Henry's treacherous decision to kill 13 men whom they could not repay. He fears their past may come back to ruin his reign.
Mary meets Robert Dudley. He promises himself fully committed to their union and proposes. Mary accepts. Later, she's in bed with Gideon, her engagement ring removed. She tells him of her distant cousin, Joseph Tudor, who would be the next male in their family in line for the English throne. Gideon promises to find him so that Elizabeth will have to name him her successor. Dudley spies Gideon coming out of Mary's room and tells him to end their affair.
Gideon finds Joseph Tudor and learns, before ever coming inside, that Tudor has been meeting with the Vatican. Mary's theory is correct.
Greer meets with her sister and brother-in-law when he receives a letter. They're being blackmailed. Someone knows that Greer's sister isn't pregnant and that Greer is the one giving birth. Greer suggests paying the blackmailer.
Bash, Catherine, and Charles discuss whether it may be possible that the current Red Knights threatening her are descendants of the original Red Knights whom Henry had killed. Bash is sent to a brothel to track down the theory. While he talks to the madam, he spies one woman dodging the questions and learns that one of them gave birth and left the baby in the woods to die. Bash finds a man whose legend states that he is the son of a Red Knight.
Gideon confirms with Mary that the Vatican planned to put Joseph Tudor on the throne. He tells her that he is returning to England with Tudor to take him back to Elizabeth, but the Archibishop stops him before Gideon can get into his carriage. Gideon is arrested.
Leith visits Greer in her tavern. She reveals her pregnancy to him and asks for his help. When he tells Claude he can't go to Paris with her on a romantic getaway because he has to help Greer, she decides she's coming along with him on his trip to stop the blackmailer.
Mary learns that Gideon has been arrested. She shares her entire plan with Catherine in hopes that Catherine can help her. Catherine points her in Robert Dudley's direction. Dudley visits Gideon in the dungeons and learns of the assassination plot against Elizabeth. He agrees to go in Gideon's stead.
Bash meets with the man from the battle ring and learns that the man has recently been approached by a group who call themselves the Red Knights who want revenge on the Queen Mother. Bash and the man hear a horse outside and when they step outside, the man is killed. Bash shoots the man on the horse and takes him home to Catherine.
Dudley returns to England and finds Elizabeth and Lola playing chess. Elizabeth meets with her advisors and lets them know Joseph Tudor, the traitor, will be drawn and quartered. She vows not to name a successor and rescinds her offer of succession to Mary. Gideon is released from the dungeon. Mary lets him know the Vatican will be approaching Catherine to ask for Gideon's head.
Catherine questions the man Bash brought in from Dijon with Christophe's help. Christophe tortures the man while Catherine asks the questions. The man refuses to speak except to say that the Red Knights aren't coming for Catherine but for the entire House of Valois. The man throws himself on Christophe's blade.
Leith and Claude follow Thomas and find him in a tavern instead of meeting with a blackmailer. They learn that Thomas and Greer's sister planned to move to Switzerland with the baby. She forces them to leave her establishment and refuses to give them the baby.
Mary meets with Catherine and asks for help saving Gideon from the Vatican. Catherine comes up with a plan that will save Gideon's life, but it will involve Gideon going back to England. Mary will lose him. Mary tells Catherine to make the trade. Dudley tells Elizabeth the truth about Gideon's involvement in uncovering the assassination plot.
Catherine intercedes with the Archbishop and when he gives her pushback about whether or not she asked the men of court for permission, she stands up to him. Then she makes an appeal to Narcisse to have him on her side knowing he loves his country more than he hates her.
Later that evening, Catherine receives a visit from Christophe who has disposed of the body of the man they killed. For him, their encounter with the man in the cellar was foreplay.
Claude offers to help Leith rise in his station by agreeing to set up meetings for him with nobles who may be able to help. Mary says goodbye to Gideon and Agatha.