On the latest episode of period drama "Reign," the castle is under siege, and the characters have to think on their feet to try to survive.

In "Left Behind," Italian nobleman Count Vincent (Michael Aronov) is bitter at the French for taking his only son prisoner. Although his son was released, he died of dysentery on his way back to Italy, and the Count believes it was due to the horrible conditions in the French prison. The Count and his men lay siege to the castle to exact his revenge. 

King Henry (Alan Van Sprang) is off with his men on an errand, so it is up to Francis (Tony Regbo) to take charge, especially since Bash (Torrance Coombs) has been taken prisoner and is in the dungeon.

Francis offers himself as a prisoner to Italy in an attempt to save the others. Catherine (Megan Follows) is horrified at his proposal and offers Mary (Adelaide Kane) in his place. She says that if he takes Mary, he'll have a new wife who will be able to bear children.

While the Count considers that proposal, Catherine teams up with Mary to try to organize an escape from the castle.

Meanwhile, Greer (Celina Sinden), who is disguised as a peasant, gets into a scuffle with a guard and grabs a pan and knocks him over the head, apparently killing him.

Mary and Catherine then decide to create a distraction during the Count's feast, which will allow them to escape through the castle's tunnels.

Mary and her ladies-in-waiting attempt their escape, but Olivia (Yael Grobglas) misses her cue. They are then brought before the Count.

All of the men around Catherine then keel over and die. It's revealed that she poisoned them using the gold to pay her ransom.

Vincent then decides he's going to rape Mary, and Catherine is furious, demanding that the Count unhand her. Mary acts quickly and stabs the count with a dagger. Afterwards, Francis enters the room and chops off the Count's hand.

Catherine reveals that she was raped by a gang of men in the past, and that her rescuer arrived too late. Catherine tells Mary never to wait for a man's rescue.

It's later revealed that Bash's mother, Diane de Poitiers (Anna Walton), is the reason for the castle's invasion. She leaked information to Count Vincent about when Henry would be away from the castle. She is insistent that the line of succession be changed so Bash is the next heir to the throne. 

The episode ends with Mary asking Francis why he came back for her instead of escaping through the catacombs. He tells her, "Because I love you." He decides that their engagement is back on. They proceed to get into bed, where their relationship is taken to the next level.

On the next episode, "Fated," "Nostradamus tells Mary of his prophecy that one among them will die soon, which causes Mary to make a decision that will forever change her relationship with Francis. Clarissa becomes bolder with her endeavours, while Kenna informs Catherine of Diane's plan for Bash, which ends up backfiring."

Check out the promo for "Fated," which is the mid-season finale of the series. "Fated" airs Thursday at 9 p.m. EST on The CW.