Moments after Kato returns from his business trip and steps out of the bullet train, a hostage crisis occurs on the same train. The suspect has taken hostages and, for some reason, begins live streaming his actions on the internet. While the First Investigation Division and Special Forces arrive on the scene, Kato discovers that the suspect is the same young man that was sitting next to him in the train. The First Investigation Division decide that they have no choice but to shoot the suspect, but Kato tries to talk them out of it. However, due to an incident caused by Kato in the past, his pleas fall on deaf ears.

On his day off, a family situation leads Daisuke to break out of his own mansion. Shortly after he steps out, Kato calls him to help a young boy who is distraught over a lost dog. Daisuke realizes that he left his wallet and gadgets back at the mansion. Unable to resort to his usual tactics, they have difficulty finding the lost dog. Daisuke doesn’t want to go home, so Kato reluctantly invites him into his apartment.

The president from the Republic of Poliador arrives in Japan, and the Modern Crime Prevention Task Force are assigned to assist the First Investigation Division in protecting the embassy from the outside as security personnel. Daisuke is invited inside the embassy as a representative of the Kambe Group. After the dead body of an embassy employee is discovered inside the building, the president and Daisuke are forced to evacuate to the panic room. Daisuke traces the footsteps of the suspected killer by hacking into the surveillance cameras. Kato finds the suspect as he attempts escape and tries to apprehend him.

Kato takes the heat for the handling of the embassy case. Daisuke checks out the device left behind by the suspect, but for some reason his AI butler, HEUSC, refuses to listen to his commands. Cho-san also investigates articles left behind at the crime scene and pursues the case from a different angle with the help of Kato. Their investigation leads them to a woman named Imura who works at a manufacturing company. However, Daisuke’s actions interfere with their meeting with the woman.

When Cho-san was a member of the First Investigation Division 19 years ago, he and Takei were assigned to investigate the murder of Daisuke’s mother, Sayuri. At the time, Cho-san entered the Kambe residence to investigate, and Shigemaru, the head of the Kambe family, surfaced as a suspect in the case. However, the investigative task force folded due to pressure from the top brass of the police, and Cho-san was demoted. Now back to the present, after the mysterious death of Imura, the woman who Daisuke brought into the police station, Kato and Cho-san’s suspicions deepen, so they decide to enter the Kambe residence.

Daisuke locks Takei up in the basement of the Kambe residence. Cho-san interrogates him to find out who the mastermind is behind all of this, but Takei is shook with fear and refuses to speak. Daisuke discovers that the reason why HEUSC is being uncooperative is related to his parents’ research. Kato goes through the documents that Cho-san gathered in his 19 years of investigating the case and finds an important photo.

Even after those people were murdered, Daisuke claims that this incident is an internal problem of the Kambe family. The rift between Daisuke and Kato has become so serious that they decide to go their separate ways. However, Kato is apprehended by the First Investigation Division as a material witness. The remaining members of the Modern Crime Prevention Task Force follow the clues about the suspect that Cho-san left behind. Suzue claims to have seen the actual suspect inside the Kambe residence, and clearly states that it was none other than Shigemaru Kambe.

Aboard the cargo ship headed for Poliador, a terrorist named Weinski relentlessly attacks Daisuke and drives him into a corner. With all his new gadgets disabled, Daisuke finds himself in a pinch but is saved by Kato. They join forces again to escape from the ship. Meanwhile, at the Kambe residence, Suzue determines that the engine of the ship is being powered by a new energy source developed by Shigemaru.

After escaping from the cargo ship, Daisuke and Kambe pursue Shigemaru and arrive at the old site of the 3rd Laboratory owned by the Kambe group, which is the source of all the mysteries. Daisuke confronts Kikuko, the head of the family, with his burning questions, but her answers force him to make a crucial decision. The truth behind the tension and conflict between the three generations of the Kambe family becomes clear.