In “Mercy,” Mary (Adelaide Kane) longs for justice after being raped in the previous episode, and Francis (Toby Regbo) is hell-bent on revenge for those who defiled his wife. So, for the sins of a few Protestant radicals, all must pay.
Francis rounds up well-known Protestants and throws them in the dungeons. He does a line-up of men, and Mary looks at all of them but can’t identify her rapist. Mary, struggling with what happened to her, moves out of her bed chambers. Her ladies-in-waiting are confused by her behavior, and Mary admits she was raped.
Lola (Anna Popplewell) goes in search of Francis, feeling guilty that she didn’t help Francis trap Narcisse (Craig Parker) and offers up a place where Francis and his men might find him. Francis goes to Mary and tells her his plan and he also finally confesses to her what has been going on. He tells her he was the one who killed his father and Narcisse was blackmailing him – threatening not only Francis but Mary and his mother Queen Catherine (Megan Follows).
With Francis gone, Mary is still on a mission to find her rapist. When she and Conde (Sean Teale) get a lead, they decide to seek out the wife of the man who funded the radicals, and Mary insists on coming along. With the help of the dead man’s wife, Mary and Conde track down some men believed to be involved in the raid on the castle.
When Conde corners the men, Mary arrives and is shocked to come face-to-face with her rapist. At first, she tells the man he will have to come back with them and hang for his crimes. She adds that his existence will fade from history, but she will live on and be known for ages to come. When the man goes on a rant about how he will be forgiven by God, Mary lets her anger take over and throws a lit lantern on him, burning him alive. She tells Conde to kill all the men and let them burn for their sins.
Meanwhile, Greer is dealing with her husband Castleroy (Michael Therriault) being punished for his Protestant ways. When Leith (Jonathan Keltz) comes to arrest Castleroy, Greer begs for forgiveness. With Castleroy in jail, Leith acquiesces to Greer’s pleas and talks to Francis. Leith reminds Francis that he promised him he would help him if he asked, and Leith is asking for Castleroy to be released. Surprised, Francis asks Leith if he is absolutely sure; Leith says yes.
Once Castleroy is released, Greer tells him to take his children and flee. As for her, she has to stay in the castle. She says she has responsibilities to Mary and will make sure Castleroy stays safe.
As for Catherine, she continues to see her dead twin daughters and fears for her other daughter Claude’s (Rose Williams) safety. As a child, Claude killed her twin sisters by placing flowers in their throats. These same dead sisters are longing for revenge, and they warn Catherine that if she doesn’t kill Claude, then they will.
Catherine is seen placing some kind of liquid in soup meant for Claude. Later, Bash (Torrance Coombs) finds Claude out of sorts and running a high fever. Is Catherine slowly killing her daughter Claude?
At the close of the episode, Mary is feeling guilty about what she did and tells Francis that she blames him for what happened to her. She knows it isn’t fair, but she can’t shake the feeling. She decides that they will be a couple in public, but will live separate lives. Francis vows he won’t live like that as Mary walks away.
Settling in her new chambers, Mary is handed a letter by a servant that was found in her room under a rug. It is a letter from Conde stating he won’t marry Claude because he is in love with her.
But does Conde have genuine feelings for Mary, or is he just trying to romance her for his own hidden agenda?