Holmes and Watson investigate a mass murder when a chef and his patrons are poisoned after dining on a tasting menu tainted with snake venom. Also, Detective Bell's crush on a work colleague makes Holmes realize his and Fiona's relationship is at an important crossroads.

Joan worries Sherlock's sobriety is at risk when she learns he has been lying to her about attending recovery meetings. Also, Sherlock and Joan discover a man's death caused by ingesting poisoned sausage is connected to a lab working on a breakthrough in the artificial meat industry.