When The CW's historical fiction romance series "Reign" returns with an all-new episode, Mary, Queen of Scots, will face new adversaries trying to strip her off her crown. This evil plan will bring death, but will it be the Queen of Scots?

As revealed in the synopsis of episode 13 of the fourth and final season of "Reign," titled "Coup de Grace," Lord Darnley (Will Kemp) will connive a plan to dethrone Mary, Queen of Scotts (Adelaide Kane). He will scheme Mary's downfall with the Scottish clergyman John Knox (Jonathan Goad). The pair's evil plan will cause the death of one of Mary's friends.

In the trailer, the clergyman proposes the idea, telling Lord Darnley that she will continue to ruin the land as long as she draws breath. "So you want to kill her?" Darnley responds.

Elsewhere in the episode, Queen Elizabeth (Rachel Skarsten) will have to remove Gideon Blackburn (Ben Geurens), the English envoy in France who is tasked to seduce the Queen of Scots from her court if she wants to keep her suitor. Elizabeth's husband-to-be, played by Steve Byers, made this request. Meanwhile, in French court, Charles (Spencer MacPherson) will make Henri (Nick Slater) know that he is firm on his stance.

From the looks of it, Mary will have no problem removing Gideon from court, as the upcoming marriage will secure her throne and grant her more power.

The upcoming episode "Coup de Grace" was penned by John J. Sakmar and Kerry Lenhart. Meanwhile, Megan Follows, who plays Catherine de Medici on the show, directed the episode.

The CW's historical fantasy first premiered in 2013. The present season of "Reign" will be the show's last. The last installment of "Reign" consists of 16 episodes.

"Reign" season 4 episode 13, titled "Coup de Grace," airs this Friday, May 19, at 9 p.m. EDT on The CW.