Lloyd Springer hires Sherlock and Joan to locate Dr. Vincent Bader, who Springer blames for getting his son Brian hooked on prescription painkillers. Bader's wife reveals that her husband was a devoted "prepper," a survivalist preparing for the inevitable apocalypse.
Bader's colleague, Dr. Wallace, directs them to a drug rep, who reveals that Bader had bene selling drugs out of his practice to a gang. After an auditing scare, he swore that he broke things off with the dealers.
Bader's body turns up, and it appeares that he was killed with a survivalist's multi-use tool. They learn that he had spent $100,000 on joining "The Keep," a luxury bunker for rich people to endure the end of the world.
Sherlock and Joan visit the bunker and swiftly expose it as a fraud. They also find the scene of the murder outside the bunker's infirmary.
Sherlock reveals that Bader was attempting to steal The Keep's pharmaceutical stores to replace the drugs he had sold from his own practice, but there were no drugs at the bunker. His partner, Wallace, realized that whatever happened meant the end of his career, so decided to kill Bader.
Meanwhile, Fiona breaks up with Sherlock over what she sees as his treating her differently. After he explains her misconception, she propositions him to have sex for the first time in their relationship.