Holmes and Watson have entered into a mutually beneficial arrangement with Shinwell Johnson, an ex-convict who shared his expertise of the city's underworld in exchange for them teaching him how to be an effective FBI informant. The trio's alliance ended when Shinwell attacked Holmes after he and Watson discovered Shinwell committed an unsolved murder. The assault caused Holmes to suffer memory loss and hallucinations, a secret which compromises his work and relationship with Watson, and forces him to seek neurological help. Holmes copes with his health crisis by refocusing on his sobriety and discovers a new ally in Michael, a fellow addict who once found the strength to stay sober from Sherlock's own words in past meetings. As Holmes struggles with uncharacteristic vulnerability, he fights to salvage his career and his friendship with Watson, which he values above all else.