Bang bang! In the middle of a bank robbery, they hear what sounds like a gunshot coming from the basement of the building. Several members of the gang rush to the scene and find the dead body of their leader, Mr. White, inside the vault!
There was a bullet wound in his abdomen and a bruise on his head. He was leaning against the wall, dead, still clutching the gun in his hand. A bloody baton was lying nearby. The bank branch manager was also in the same room, but his hands and feet were tightly bound with cable ties and he was unconscious, so it was unlikely that he was the culprit. All the other hostages on the first floor were under strict guard.
In other words, the only possible suspects are the five members of the robbery gang who are able to move freely within the building. Is there a traitor? Has an undercover agent infiltrated the group? If so, it would be dangerous to flee back to the hideout. They must track down the culprit and clarify the situation as quickly as possible. As the time limit for escape approaches, the members must carry out physical searches on each other, question the hostages, and investigate the corpse and the surrounding area at lightning speed!
—description from the publisher (translated)