Synopsis for 3×19: Sherlock ends up helping a hacktivist from the collective Everyone, and it turns into a murder investigation. Joan struggles to get back into the swing of being social and appears to be trending toward isolation as she comes up with excuses to avoid a bachelorette party.
While practicing heart rate manipulation, Sherlock was rudely interrupted by his latest client pounding on the door. Much to his surprise, the young man on his doorstep claimed to be a hacker from the infamous hacktivist group Everyone, which has been mentioned throughout the show’s existence. They’ve forced Sherlock to embarrass himself on multiple occasions, but at this point the man who goes by SuckingChestWound (later revealed to be named Petros) needs Sherlock’s help to keep a civil war from blowing up.
According to Petros, there’s another leader who opposes him on a lot of issues. While Petros wants to continue along the lines of disorganized anarchy, Species, the other user, wants to organize Everyone into a collective with set parameters. Species wants Everyone to be an organization that goes after specific targets for political reasons, not just for fun. Petros wanted Sherlock’s help to track down information on Species but was turned down.
The next day, Species turned up very dead, and Petros was certainly the prime suspect.
Sherlock turned to the video surveliance they’ve got around the brownstone and was able to find good video for the NYPD. He was also able to find the gum, which Petros had been asked to take out of his mouth before stepping foot into Sherlock’s home. The gum had been wrapped in a piece of paper with a song list with oddly specific sound information. From that, Sherlock came to the conclusion that Petros had to be some sort of sound engineer and they were able to track down the club he’d last DJ’ed for.
When they brought him in, he claimed he had an alibi for the night that Species was killed. He gave the name of an investment banker who had a tendency to hang around the Everyone message boards. According to Petros, the two had been sleeping together that night and she would alibi him. Of course she didn’t.
As all of this is going on, Joan got sucked into a bachelorette party that she clearly didn’t want to go to. Even after she went, she made up an excuse to leave early and returned to working on the case, piquing Sherlock’s curiosity.
Sherlock lured the investment banker to his home, since she had been reluctant to give them information at her place of work. She admitted she had denied she was with Petros that night to save face about the fact she was cheating on her husband with Petros. With an alibi, Sherlock came to the conclusion that Petros was being used as a patsy and there was something far more nefarious going on.
Put on the trail of Everyone’s “Inner Sanctum” they began to search for someone who could have profited off of his death. One of the members was tracked through a recent motorcycle purchase, and a bit of investigation revealed that the man behind the screen name, Caleb, had suddenly come into a great deal of money. It quickly came to light that, while he had stolen Species’ “stash” of information and sold it for a nice profit, he hadn’t killed the guy.
Sherlock finally confronted Joan about her strange, isolated behavior. He tried to come at the situation by claiming it didn’t “work for him” for her to be acting so much like him. However, she didn’t take it well and essentially told him to butt out. It was what she needed to do at that moment and she didn’t wish to be critiqued.
With a bit more poking around, Sherlock and Joan came to the conclusion that there were two different people running Species’ account. Automatically the other user involved became a prime suspect. To add to it, whoever was running Species’ account was dead set on launching an attack against a conservative group called the Atherton Think Tank. Joan and Sherlock showed up there and tried to warn them, but found the man they talked to didn’t seem too worried. As they left, Sherlock proposed that the think tank wasn’t a think tank at all, but may have connections to higher government entities.
Sherlock revisited Joan’s odd behavior and they had a talk about friendship. He let her know he’d been observing her taking on more of his own attributes and said, “I am not a better person because of a lack of connection.” He wanted to encourage her not to follow in his footsteps. Rather, they need to be one Holmes and one Watson. Anything else would lead Watson down an undesirable path.
With some brilliant detective work, Joan lured the other user behind the Species handle into revealing himself. Brady is the man they tracked down, only to be interrupted by an FBI agent who was determined to keep Brady out of their hands. She alibi’ed him for the night of Species death, leaving Sherlock and Joan to puzzle over the situation.
With more digging it was revealed that the Atherton Think Tank was a digital analysis group for the NSA and exposing them would not only embarrass them, but leak government secrets. Sherlock realized that Agent Branch, the FBI agent protecting Brady, would have a lot to gain if that were to be the case and the secrets were to be exposed. So Sherlock approached her with leverage.
They found that Agent Branch has hired an illegal nanny to take care of her child and used it to get her to give up the murder weapon. She would rather have kept her career intact than have it destroyed by bad publicity. Brady was arrested, and the case was solved.
Joan, having taken what Sherlock said to heart, agreed to be back on the bridal party for her friend’s wedding.