Plot summary
King Francis has another collapse, and the news spreads to various parties, including King Antoine of Navarre and Nicholas, newly-arrived ambassador of England. King Antoine has come to King Francis to ask for help, and is told to sign away his claim to the French throne in return. Queen Mary releases her mother-in-law from prison to help block Nicholas's attempts to interfere; they are successful and King Antoine signs away his claim. Prince Charles accidentally causes his friend, Constance (Jordan Monaghan), to overdose on opium, but she is saved with Princess Claude and Lord Narcisse's help.
King Francis learns of Narcisse's helping Charles and gives his blessing for Narcisse and Lola to wed immediately. Leith lets it slip to Claude that he is afraid of developing feelings for her. Mary realizes that the alliance with Scotland is too damaging to France, so she decides not to marry Prince Charles after King Francis dies, but sets her sights on Don Carlos of Spain. King Francis and Queen Mary decide it is best that Queen Catherine be the regent after King Francis's death.
Credits
Adapted from Wikipedia contributors, Reign season 3. HTML formatting and reference markers removed.