The episode "LOCK ON," Dr. STONE season 4 episode 8, opens with a flashback showing Dr. Xeno awakening from petrification. He immediately begins searching for other survivors, demonstrating a calm but determined demeanor. Xeno discovers nitric acid, which becomes the key to reviving people from petrification. He uses this discovery to revive Stanley, who is significant to his plans. Together, they revive others who remained conscious during petrification and start building their colony. Xeno's discovery of a platinum ring allows him to mass-produce nitric acid and gunpowder, enabling the creation of firearms and weapons. They construct a large warehouse dedicated to manufacturing gunpowder, signaling the militarization of their group. This flashback contrasts Xeno's use of science for domination with Senku's use of science for preservation and progress. Xeno is shown wearing a black coat, symbolizing his darker ambitions, while Senku wears white, symbolizing hope and life.

The narrative then shifts to the present, where Stanley is hidden in the trees, waiting for Luna to give him a signal to shoot. Luna, who is disguised as a spy aboard the Perseus, is tasked with locating Taiju and luring him out so Stanley can assassinate him. Luna successfully finds Taiju but struggles with the decision to signal Stanley. Instead of immediately betraying Taiju, she shares information about Senku's presence on the ship with Stanley. Meanwhile, Senku notices Luna's suspicious behavior and decides to charm her to extract information about Xeno and his forces. Before Senku can get much information, Ryusui and Francois interrupt. Ryusui requests something desirable for Luna, leading Senku and Francois to make ice cream for her, which she enjoys. This moment of levity contrasts with the tension of the spy mission. During this interaction, Senku realizes that Dr. Xeno is his former mentor from childhood, a NASA scientist who inspired Senku's passion for building advanced rockets. This revelation adds a personal dimension to their conflict.

Senku's plan is to use the information extracted from Luna to send an encrypted message to Tsukasa's special squad, alerting them to the threat posed by Xeno's forces. Ryusui remains suspicious of Luna, suspecting her true allegiance. Luna's hesitation and the information she provides create a tense atmosphere aboard the Perseus, as the Science Kingdom prepares for the impending confrontation with Xeno's Empire of Might. The episode builds suspense around the spy mission and the looming battle, emphasizing the strategic moves by both sides.

The episode ends with the tension escalating as Stanley remains poised to act on Luna's signal, and Senku continues to gather intelligence. The stage is set for a dramatic clash between Senku's Science Kingdom and Xeno's militarized forces, highlighting the ideological and personal stakes of their conflict. The episode's final moments underscore the fragile balance between trust and betrayal, science and warfare, as the characters prepare for the next phase of their struggle.

Episode 8 reveals that Senku and Xeno once shared a mentor-student relationship, with Xeno being Senku's old science mentor from childhood who helped spark Senku's passion for building advanced rockets. However, they have become sworn enemies, as Xeno pursues ambitions of dictatorship and weapon manufacturing while Senku uses science to save lives.

Xeno discovers nitric acid, which is key to reviving people and manufacturing weapons. He also obtains a platinum ring, which provides the necessary material to create munitions. Using these resources, Xeno builds a fortress and a warehouse to produce gunpowder and guns, making him a deadly threat.

Luna is sent by Stanley to infiltrate the Science Kingdom crew and locate Taiju, with the goal of luring him out so Stanley can kill him. Luna succeeds in finding Taiju but struggles to give Stanley the signal to shoot. Senku interacts with Luna, charming her to extract information about Xeno and his forces, while Ryusui and Francois also engage with her, even making ice cream to gain her trust.

Stanley is a loyal subordinate to Xeno, tasked with eliminating Senku and the Science Kingdom's leaders. The episode and related commentary suggest that Stanley and Xeno share a close, possibly romantic relationship, indicated by their intimate interactions and long-standing connection. This adds depth to their alliance and motivations.

The episode contrasts Senku and Xeno's approaches to science: both discover nitric acid around the same time, but Senku uses it to save lives and advance civilization, while Xeno weaponizes it to take lives and pursue dictatorship. Their differing coats--Senku's white and Xeno's black--symbolize their opposing philosophies and moral outlooks.