In the fourth episode of "The Most Heretical Last Boss Queen: From Villainess to Savior," the story unfolds with a sense of urgency as the characters attempt to rescue survivors from a disaster. The episode begins with the aftermath of the death of Rodrick, the captain of the knights, who lost his life while protecting the new recruits. The characters express their grief and shock, with one figure, Rodrick's son, vowing to avenge his father's death.

The son, who is not a knight, feels helpless and decides to train and act like his father in order to become a knight himself. He is determined to bring justice to the woman he believes is responsible for his father's death. Amid his resolve, the scene shifts to a surprising rescue. The sky becomes visible, indicating that they have been saved from the disaster. The savior turns out to be the first princess of the country, Her Highness Pride Royal Ivy.

The episode then delves into the aftermath of the rescue. The knights are shocked to learn that their savior is the first princess of their nation. They thank the princess for saving them but also express their concern over her involvement in the incident. The princess, however, defends her actions, stating that she wanted to save the knights, who are the beacons of the country.

Additionally, this episode introduces a new character, Arthur Bersford, the son of the captain of the knights. Arthur expresses his desire to become a knight like his father and asks the princess if he can achieve his goal. The princess encourages him, saying that he can become an honorable knight like his father.

The episode ends with Arthur making a vow. He promises to protect the princess and eliminate anyone who tries to deceive or stand in her way. He swears to do everything in his power to save her, just as she saved him.