Sucking Chest Wound from the hacking group, Everyone, wants to hire Sherlock to dig up dirt on his rival, Species who is trying to lead the group in a different direction. Sherlock declines.
Detective Bell calls Sherlock. He's at a murder scene that has a connection to Sherlock. It's Species. Sherlock finds a pink hair that belongs to Sucking Chest Wound.
Sherlock finds the piece of paper with Sucking Chest Wound's gum in the garbage. The paper was a play list. Sherlock eventually deduces that Sucking Chest Wound is a sound engineer and Petros Franken is his real name.
Detective Bell questions Petros and he denies killing Species. He claims he was with Mockingbird, Rachel Carter, when Species was murdered. Bell and Sherlock question her and she denies being with him. They find Species blood in Petros' trunk.
Joan has dinner with friends to plan a bachelorette party. She pretends Sherlock needs her as an excuse to leave.
Mockingbird comes to the brownstone. She lied because she is married but admits she was with Petros.
Sherlock visits Petros in jail. The motive lies in Species; Petros is just the patsy. Petro tells Sherlock about Species Stash which included credit card numbers, social security numbers etc. He suggests they investigate the inner sanctum of Everyone.
Monkey Versus Shark stole Species Stash but didn't kill him. He tells Sherlock and Detective Bell that the stash included more than credit card numbers, but information on every hack and conversation Species had.
Sherlock confronts Joan about pushing away her friends, which she denies.
Sherlock figures out there are two Species from their communication style. Tessee is the other Species. By killing Species, she strengthened his cause while destroying Petros side.
Sherlock and Joan visit Petros in jail and ask him about Operation Right Nut. It involved hacking Atherton Foundation, a right wing think tank. Species thought it was too dangerous.
Sherlock apologizes to Joan. He tells her that his tendency to isolate himself is a mistake that he doesn't want her to repeat.
Joan and Sherlock confront Brady Dietz who they believe is Tessee. The FBI intervenes and takes Dietz away. He is their informant and Agent Branch alibis Dietz for Species' murder.
Sherlock has an Forensic Accountant look at Atherton's records. He uncovers their relationship with the government. They surmise Agent Branch wants Everyone to hack Atherton, which will make it a RICO case and help her career. Sherlock confronts Branch. He wants her to anonymously deliver the murder weapon or he will tell the FBI about her illegal Tibetan nanny. She agrees and Dietz is arrested.
Joan leaves to join her friends for dinner and to plan the bachelorette party.