Holmes and Watson meet their match when they deal with a group of activists protecting a civil engineer who leaked classified information. For the first time this season, Moriarity is brought and how Sherlock has dealt with Irene being Moriarty. Sherlock admits he is post love. While Watson looks for love on an online database. When they're lives are taken over by the online activist group "Everyone" Joan and Sherlock must go "dark" and learn to solve the case without the use of technology. In the end, Joan uses a "slip of a hand" to frame the leaker proving that she is more than just a good student. All the while, it is revealed that Sherlock has been receiving letters from Moriarty.