Plot summary
Elizabeth is scared that if Darnley, a Stuart cousin of Mary, marries Mary, then their offspring would have an undeniable claim to the throne of England since both Mary and Darnley have the same paternal grandmother of the House of Tudor and both of the child's parents would be Tudor/Stuart royals. Gideon, with Elizabeth's blessing, goes to Mary with a proposal: if Mary marries him and abdicates, Elizabeth will make their firstborn son heir to the throne of a united England and Scotland. (However, Gideon has secretly promised to Elizabeth that his marriage to Mary would attenuate her claim to the English throne since Gideon is a commoner.) Mary is ready to accept, but changes her mind after meeting Lady Lennox, who shares her past experience of being Elizabeth's prisoner.
Lady Lennox (daughter of Margaret Tudor) also sabotages Darnley's attempts to be with Keira, who is married off to someone else. Narcisse returns to French court and works with Catherine to remove Leeza's Spanish choice for Chancellor of France. Catherine and Narcisse send a young woman, Bianca (Sofia Banzhaf), to Charles in the hopes of rejuvenating him, but she disappears. Claude finds solace in religion in the wake of Leith's death. James pursues an affair with Emily Knox (based on Margaret Knox ).
Credits
Adapted from Wikipedia contributors, Reign season 4. HTML formatting and reference markers removed.