Gregson's daughter Hannah comes to his office to talk to him. Firefighters discover Ando Azuma, a dead Japanese IT consultant, at a fire scene. Sherlock discovers the killer took retired Kakuza Ando's artificial finger. Sherlock and Marcus interview the woman who built his artificial finger, and she explains the missing digit included a flash drive. Gregson tells Joan that Hannah is an alcoholic and wants to know how to help her. Mason cracks Ando's dark-web account. Sherlock and Joan go to visit Go Shinura, who had been paying Ando for a gambling debt. Shinura said he had seen Ando robbery a warehouse recently. Sherlock and Joan go to visit the warehouse, where they get busted by the U.S. Air Force. The Air Force officers admitted Ando was helping them up their technology for the nuclear-missile control network. So Ando may have had data about the program on his pinky drive. Joan finds insiders opposed to the upgrade, and thinks one of them may be responsible for Ando's death. One such insider was General Alvaro, but he had an embarrasing alibi. Alvaro pointed them to Eddy Dunbridge, a used computer-parts salesman who benefits from the Air Force's current system. Michael hits Hannah's car, and exchanges information with her. Marcus and Sherlock find Eddy got stuck in his boat escaping from people trying to kill him. Sherlock and Gregson has an uncomfortable talk about Hannah. Two of Dunbridge's old floppy discs have the formulas for printing U.S. currency, one of which made it to the Air Force. One of the officers figured out what the discs contained. They suspect Col. Deakins, who has no sense of smell and wouldn't have smelled the food on the stove which set Ando's apartment on fire. Shinura set up Deakins for the police. Michael kills Hannah's roommate.