"Ray of Despair, Ray of Hope" is a mix of unexpected revelations and intricate plot maneuvers. The episode begins with Senku and his crew sailing to a deserted treasure island, which they previously believed to be uninhabited, and devising a cautious plan to use an approaching storm as cover for their arrival.

The landing team, consisting of Senku, Soyuz, Kohaku, and Gen, is sent to the island to avoid potential conflicts with any locals they might encounter. Meanwhile, Ukyo, who stays behind on the ship, sets off on his own to explore the seabed after detecting an anomaly with the sonar.

The crew of the Perseus discovers Suika, who had stowed away on the ship and is desperate to participate in the mission. At the same time, Ukyo and Ginro stumble upon a horrifying sight—petrified corpses beneath the sea. The presence of these corpses suggests that the petrification occurred after they landed, hinting at a possible threat on the island.

Shockingly, Soyuz observes through his telescope that the remaining crew members aboard the Perseus have been petrified. The sole survivor of this sudden catastrophe is Suika, who had been thrown overboard by Ryusui out of concern for her safety.

The plot then introduces a new character named Amaryllis, an islander whom the reconnaissance team follows to gain insights into their surroundings and locate the supposed treasure. As Senku and his team engage with Amaryllis, she gradually realizes that her true intentions do not align with her impending arranged marriage to the mysterious "Master."

The story takes a turn when the villagers rebel against the Master, prompting Senku to deploy the tear gas he had prepared as a precaution. When Amaryllis witnesses this "sorcery" and understands the team's goal of saving the petrified, she reveals her knowledge about the source of the petrification beam. Additionally, she unveils her plan to defeat the Master in his own palace and asks Senku for assistance in her mission.