: Catherine de' Medici (Megan Follows) sees her storyline conclude in a "completely Catherine" fashion, involving a dark deal with a witch and a bizarre ménage-à-trois to protect her power and her mentally fragile son, King Charles. The Execution and The Afterlife All It Cost Her - Reign Wiki
The finale spans decades of historical events condensed into a single hour of television. It begins in Scotland, where Mary is dealing with the aftermath of her son’s kidnapping by her husband, Lord Darnley. [S4E16] All It Cost Her
: To secure her son's future and her own safety, Mary makes the fateful decision to have Lord Darnley killed, an act that ultimately provides her enemies with the leverage needed to turn Scotland against her. : Catherine de' Medici (Megan Follows) sees her