Plot summary
The bodies of the recently-executed Protestants bear the marks of the dark riders, so Cardinal Perazzo (Bruce Ramsay) concludes that Protestants have this mark to declare their extremism. He orders Louis's arrest since he has the mark, so Queen Mary helps the Prince escape to Antoine's estate. Antoine tells Prince Louis that their agenda is best served if Prince Louis seduces Queen Mary, but he refuses.
When the Cardinal's men arrive to arrest Prince Louis, Queen Mary and Leith have the mark burned away. King Francis and Bash work together to undermine Cardinal Perazzo by putting the mark on his lover, forcing the Cardinal to recant his stance on the mark's meaning. Lady Kenna investigates her suspicion that Queen Catherine is poisoning Princess Claude, and learns that the Princess and Bash were once lovers. Princess Claude confronts her mother, who confesses to the poisoning because she believes that Claude killed her infant younger sisters, but Princess Claude claims that she did no such thing. Queen Mary remains distant from King Francis, despite his efforts to offer comfort and peace.
Credits
Adapted from Wikipedia contributors, Reign season 2. HTML formatting and reference markers removed.