Fiona, the autistic computer coder, asks Joan for assistance doing a background check on her new boss, and also asks Joan to return a book Sherlock lent her. Joan realizes that Sherlock actually likes Fiona, and maybe more than a little. Fiona and Sherlock awkwardly feel each other out, eventually agreeing to go out for coffee.
Meanwhile, Sherlock is called in by Captain Gregson to assist a colleague in the Narcotics division. Narcotics needs to find out if a biker gang leader's computer in his fortified stronghold actually contains the financial information and evidence they need before they actually raid the place with overwhelming force.
Before Sherlock can do more than formulate a basic strategy for getting to the inner office, however, their inside man is found murdered.
Sherlock determines that the detective's body camera footage was staged, and that the detective was conspiring with someone to steal the biker gang's money -- only his co-conspirator double-crossed him. Sherlock quickly figures out the identity of the co-conspirator, another detective, but how it was done eludes him at first.
Eventually he realizes that the entire footage was actually staged, as in on a set, a fake room designed to look like the gang leader's office. The other detective is then arrested for murder.