Sherlock and Alfredo examine a talking car alarm, Odin. Alfredo hasn't been able to beat it and challenges Sherlock to see if he can. He can't, yet, and Alfredo reminds him it is time to go to their sobriety meeting, which Sherlock does not want to attend.
He is saved by a knock at the door from a former co-worker of Joan's. One of her colleagues is missing, and she wants to hire Joan to find her. Joan meets with Kitty who explains that Sherlock took the case in part to get out of going to his sobriety meeting. Sherlock texts them to join him near the place where Marissa's credit card was last used.
Sherlock breaks the lock on dumpster and finds Marissa's body inside.
The coroner says Marissa died soon after she went missing and they found DNA under her fingernails that belonged to Chris Jacoby. Bell says Jacoby went missing on the same day as Marissa.
They find Jacoby has been living in the park. When they find his encampment, he has been murdered. Sherlock uncovers his hidden journal. Jacoby also received a payment from the same shell company that was paying Marissa.
The coroner says Jacoby suffered massive and sudden brain damage. Sherlock speculates that Jacoby was the participant in an illegal drug trial. Marissa was the nurse who administered the drug. The company behind the trial is cleaning up loose ends.
Marissa had 5 dosages of the drug on her, so there are four other people who have taken the drug that can lead to brain damage.
They identify the other 4 participants. One died and had significant brain damage, two are missing and one hasn't shown up to work. Sherlock fears the other 3 are dead.
Sherlock believes the pharmaceutical company was testing a time-diluting drug. Kitty calls and says that Louis Caryle emailed his co-workers last night. He is alive but in hiding.
They find him hiding in his Mother's vacant apartment, and Sherlock promises to keep him safe if he tells them everything. He agrees.
Gregon and Bell interrogate Caryle. He identifies the nurse, Marissa, and the a second person. Dr Kirke from Ubient Pharmaceuticals.
Joan stops by because Sherlock skipped another sobriety meeting. He confesses that he is struggling with the tedious nature of recovery. Joan asks what she can do to help.
The police searched Dr. Kirke's apartment but couldn't find him. Sherlock believes he knows where to find Kirke. He has attended every one of his Aunt's physical therapy sessions. He shows up and Bell arrests him.
Kirke is adamant the research needs to be published. He will accept responsibility for the illegal drug trial and deaths but won't divulge anything about the funding. It's not his employer that he is protecting but a person.
Sherlock identifies Kirke's benefactor as someone who helped him become a doctor, Jack Connaughton. He is terminally ill and refuses to admit anything.
His nurse, Brett, eventually admits overhearing Connaughton hiring two hitmen. When they go to arrest Connaughton, they find him in bed. He is alive, but unresponsive. He had taken his own drug.