Plot summary
Queen Mary and Lord Darnley send loyalist Lord Barrett ( James Gilbert ) on a secret mission to invade England and capture Queen Elizabeth. Darnley asks Mary for the crown matrimonial; when she refuses, he threatens to tell Queen Elizabeth of the plot. Queen Mary sends Bothwell and Rizzio to meet with Gideon and stop the mission entirely, and they are successful. Mary swears to Gideon that she'll not threaten Elizabeth's throne ever again. Gideon tells Queen Elizabeth of the failed coup, in the hopes of encouraging her to marry Ferdinand and protect England. Mary appoints Bothwell her bodyguard and Rizzio her advisor, so to shut Darnley out from power. Henry purposely antagonizes King Charles, though his behaviour causes Narcisse to switch allegiances to him. Queen Catherine casts a spell in the hopes of helping King Charles.
Credits
Adapted from Wikipedia contributors, Reign season 4. HTML formatting and reference markers removed.