The focus of Episode 15 of "Reign," "The Darkness," takes forward the developments of the previous episode. King Henry commits another murder. Nostradamus tries to heal Olivia. Lola's pregnancy becomes a major concern for Mary, and rightly so. Bash is unable to leave the borders of France, as Rowan's house has been marked by the dark forces.
The episode opens with King Henry reminding Kenna of their deal. She pleasing him, sexually and he will return the favour by introducing her to a rich, eligible bachelor. King Henry wants Kenna to indulge him and introduces her to Anna, a paid girl. Anna offers Kenna a cup of drink. She kisses her and slips off her dress. When Kenna wakes-up in the King's bed, she finds herself tied to a dead Anna. King Henry has choked Anna to death. Kenna informs Queen Catherine that King Henry has murdered Anna.
Mary wants Lola to attend the First Light feast and meet potential suitors. She believes that marriage is a quick solution to Lola's problem. Lola assures Mary that she has no interest in becoming a future King's property, because she made an enormous mistake. Mary suggests the name of Count Philip as an ideal suitor for Lola.
At the feast, Mary introduces Lola and Count Philip. Count Philip does not take too long to tell Lola that he likes her. He also reveals that his father has threatened to take away his inheritance if he does not marry in a year's time. Count Philip would like to have a wife and an heir as soon as possible. Francis notices Lola and Philips, together, and tells Mary that he would not have picked him as a suitor for Lola.
Later, Francis visits Lola and tells her not to take words said at the fair seriously. He also indicates that he disapproves of Count Philip as a suitor for her. However, he does not provoide a reason for that. Francis wants to know if Lola is eager to marry soon because of their one night stand. Lola gives an answer in negative. Francis discloses to Mary that Count Philips prefers men in his bed. He also reveals to Mary, who looks not at all surprised, that he and Lola had a one night stand. Francis is quick to assure her that he is utterly, truly hers and there is nothing going on between him and Lola.
Mary is concerned that Francis will stop trusting her if he finds out that she knew the truth and feigned ignorance. Mary gives Lola two options either marry Count Philips or reveal to Francis that she is pregnant. Lola does not want to tell Francis about her pregnancy. Mary says that they both are suited to each other, as this Count prefers men in his bed. Lola does not want to marry a man who cannot give her happiness, but Mary is furious. She believes that Lola's mistake will destroy her marriage. Mary threatens to tell the truth to Francis if Lola does not agree to marry the Count.
When Mary enters her chamber, she finds that Francis has decorated the whole room with candles. Mary stops him from undressing her, as according to his mother's tips it is not the day to make babies. Francis tells her he does not want to make love to her because he wants a baby, but he wants a baby because he loves her. This leads to a passionate kiss between the two. The next day, Mary asks Lola not to marry Count Philip and wants her to be happy.
Meanwhile, Bash stays back to protect Rowan and her family, as their house has been marked by blood. It means a family member will be sacrificed to the darkness. Rowan has figured out Bash's true identity and his love for Mary. To beat the dark forces, Bash seals the windows of the Rowan's house and keeps only one entry point open. Rowan and her family do not want to fight, because if not them, someone else will be taken away for sacrifice. Bash is soon drugged so that he does not pick-up a fight with the dark forces. The evil man comes and takes Rowan away. Bash is unable to stop that and blames himself. He and Rowan's brother stop in front of the castle. Looking at the castle, Bash says he knows where to ask for help.
Olivia tells Nostradamus what happened to her after she had run away, betraying Mary and her friends. She was captured by the evil men and they fed upon her every night because she was already impure. Olivia does not want to return to her normal life. Later, Nostradamus baptizes her, telling her that she is new and nothing of the old remains in her.
Greer and Leith, the kitchen boy, realise that they cannot be together, as Greer has to marry someone with title. Greer receives a letter from her parents. And, Leith receives an offer of apprenticeship in Spain from Lord Peppercorn. Greer encourages Greer to take-up the offer. It is revealed that Greer had asked Lord Peppercorn to offer the job to Leith. Greer tells Lola that her parents have arranged her marriage and a carriage arrives at the castle, bringing her suitor.
King Henry is not repentant but tells Queen Catherine that he has been chosen by the God. He warns that he will teach others the lesson that he is the King and they are not, and that is why the two women were killed.