In this chapter, we learn that the police are looking for Professor Shimimura's "Shikimura file" . They're going to find it, pronto. First, they've got to figure out who sent the file to the professor's third-floor apartment. The police don't have a lot of time to find the file, so they'll have to use a public transit system to get there. They also have to find a way to spy on the professor while he's using the file. They can't spy on him, though, because the file isn't encrypted. The only way to do so is to use the "encrypted file," which the police have already figured out is inside the apartment. It's the same file that the professor sent to the third floor apartment when he was on his deathbed. So, the police need to find out what's going on with the file ASAP.