After getting suspended by Gregson at the end of the episode "M.", Sherlock decides to spend some time pursuing one of his favorite activities: riling up conspiracy theorists on the Internet. When one of the theorists goes missing, Sherlock decides to investigate on his own. After finding that the man was killed in a suspicious hit-and-run accident, Holmes looks into the victim's conspiracy theories in order to see if he had hit on anything that might have made him a target. While most of the theories are nonsense, Sherlock does find one that seems possible. In 2009, a group of people were hired by the government to devise a terror plot for a war game simulation. In all other cases, these plots were made public after the fact, but the 2009 exercise was kept classified. Now, members of the 2009 'Red Team' have started to show up dead. Fascinated, Sherlock decides to see if the conspiracy theory has merit.