On Reign Season 3 Episode 4, an urgent message arrives for Mary, but she's out sailing with Francis. Together they decipher Marie de Guise's letter and learn that Elizabeth has ordered a surge of English troops into Scotland.
Don Carlos of Spain visits Elizabeth to seek her hand in marriage. Her advisor warns her that Mary will align herself with Spain after Francis dies in order to save her country. Either Elizabeth makes the alliance or Mary will. Don Carlos is charming and Elizabeth invites him to extend his stay at court.
Catherine stops Lola in the hall and Catherine denies planting the rat in Lola's bath. Narcisse intercepts Lola and tries to sweep her away on their honeymoon. Francis, at the reminder of Charles, readies a fleet of ships to sail to Scotland's aid.
Bash visits Greer, who has bought an ale house, to warn her about the murders happening in the village. Since those who end up dead are usually weaker, he worries she or her girls could be targets. Charles is in the pub drinking with an unsavory fellow when Bash begins to feel Delphine's pain. He reveals their connection to Charles.
Robert Dudley confronts Elizabeth about her consideration of Don Carlos' marriage proposal. He begs her not to marry the Spanish prince and tells her that the secret to swaying the nobles is to make the English people fall in love with her as he has.
When Lola awakes to find Narcisse gone, only to return fully dressed with muddy boots and a story about preparing food and arranging a vineyard tour, Lola grows suspicious of her new husband.
Robert Dudley tries to send his wife, Amy, away from English court. Francis spars with Charles in order to teach the Dauphin how to fight with a sword and rule as a king. Catherine suggests they should have sought her counsel before sending French ships against the English navy, and Francis reminds his mother that the only reason she's out of the dungeon is to secure her place as regent.
Mary meets with Nicholas, the English ambassador to France, and learns that his orders are to wait for Marie de Guise and Francis to die before seizing Mary for Elizabeth. When she storms out of the room, he makes a copy of her decoder.
Catherine requests Claude's presence at a dinner where she hopes to secure enough votes to become regent once Francis dies. The Lord is unwilling to lend her his support because of an exchange which took place between his daughter and the Queen several years prior.
Greer observes Sir Nicholas decoding and copying a letter to Marie de Guise. The letter causes Elizabeth to send her forces in another direction allowing the Scottish regent to regain control of the supply route. Elizabeth, feeling humiliated, agrees to accept Don Carlos' marriage proposal.
While at lunch, Lola and Narcisse are accosted by the angry daughter of a landowner who accuses Stephan of stealing her illiterate father's land. Lola looks to Narcisse to deny the claim but he cannot.
Don Carlos asks Elizabeth why she hasn't married and tells her that there's a rumor circulating around court that she's really a man masquerading as the Queen of England. Shamed, Elizabeth storms out and finds Robert Dudley in the hall. She blames his wife for the story. He confronts Amy and nearly kills her. She begs him to stop his affair with Elizabeth and he agrees.
Lola packs her things to return to court, furious with Narcisse, when she learns that the lands he stole, combined with the lands Francis gave John, give him a vote on the privy council. He can use that vote to keep Catherine on their good side. Francis and Charles bond over the Scottish win against the English just before Francis collapses.
Francis believes he's about to die and asks Mary to lay with him so they can enjoy his final hours together.
Catherine and Narcisse walk through the halls and she reveals that she knows he planted the rat in Lola's bath. William and Elizabeth discuss her decision not to marry.
Delphine is at a convent when Bash finds her and rescues her. Charles arrives and commands both Delphine and Bash to save Francis. Mary rests with Francis and they daydream about their future together. He slips away just as Delphine, Charles, and Bash arrive. Mary begs Delphine to save Francis, so she works her magic and he returns, but the price is a life.
Across the ocean, Marie de Guise dies.