13. A Study in Charlotte

Complete story — includes the ending

A professor and some students die from consuming mushrooms tainted with a synthetic deathcap toxin. The professor's former associate, academic Alston C. Harper, says that although they had a falling out, they had made their peace. Another body, Harper's wife Charlotte Koenig, is later found. Koenig gave the professor the mushrooms. Koenig was the intended target and was producing counterfeit erectile dysfunction pills to buy real estate. The property is land a pharmaceutical company must have for a much-needed expansion. Koenig felt that they had stolen her biofuel process. Koenig would not give Harper a divorce (due to a dispute over textbook royalties). When she dropped her resistance, he became suspicious and hired a private investigator, who found out about Koenig's valuable property. Meanwhile, Joan discovers that the Brownstone's owner turned his residence into a short-term rental catering to partiers, as revenge for Sherlock and Joan's repeated disturbances of his peace over the years. After a fire breaks out, Joan uses the security cameras to prove that it was arson, thus ensuring the neighbor gets the insurance money. They also offer to pay for soundproofing and give him a jar of honey from Sherlock's bees.