An anxious Watson is buzzed into Sherlock Holmes' mansion flat above Baker Street Station. Holmes is visibly upset and reveals that he had a falling out with his brother, Mycroft. When Watson asks for elaboration, Holmes pulls Watson's phone from his coat pocket and deposits it under the cushion of a chair. He then changes into clothing suitable for fitting into a crowd, and before Watson can ask anything more, leaves the flat. Watson follows. As they walk down London's streets, Holmes fits a bluetooth earpiece into his ear and pretends to speaks into it, even though he is speaking to Watson, who is walking by him. Watson guesses that the precaution is necessary because they are under surveillance. Holmes confirms this, explaining that Mycroft has leveraged his power in the British government to create an empire of illegal dealings.
They arrive at a cabinet-maker's workshop. Holmes unlocks the heavy padlock on the door, the code to which he knows because he secretly watched an estate agent enter it the week before. Inside, Holmes shows Watson a document detailing a malware implantation plan, a sabotage program that detects typo-like programmer errors in code responsible for everyday software like computers, mobile devices, network switches, and firmware, then weaponizes them. The program also encompasses plans to obtain phone numbers, listen through phones, as well as gain access to microphones and cameras. Holmes proceeds to explain that the man who gave him the document had worked on this program. He approached Holmes because he felt the plan had been taken too far: young boys got emails with bad ideas from their Pakistani cousins, and as soon as they engaged, they were taken into retention by the US government (which was working with the British on the technology). The boys were treated as security threats, but their families were not informed—the boys would just disappear. Holmes recounts that he subsequently contacted Mycroft for help, but his brother defended the government and replied that nothing can be done. Holmes and Watson return to the flat, where Mycroft knocks on the door. After Holmes lets him in, police enter behind him.