Victorian Undead horde of zombies. Being driven to a corner while learning that shooting the zombies in the head will effectively dispatch them, Holmes and Watson are saved by the arrival of heavily armed and armored Royal Marines led by the former's brother, Mycroft Holmes. After saving Holmes and Watson, Mycroft escorts them to the surface and proceeds in providing them answers. As Holmes and Watson are being escorted, Sebastian Moran spies them from afar and travels to Whitechapel, where he reports his news to his master - an undead Professor Moriarty. At the Diogenes Club, Mycroft debriefs Holmes and Watson of
Minor Sherlock Holmes characters their relationship. She also posed as John Watson's therapist and then later revealed herself to be Eurus Holmes, and at the end of the episode shoots John Watson with a handgun. In the last episode, "The Final Problem", it is revealed that Sherrinford is in fact a high-security complex on an island to house some of the most dangerous criminals in the world, including Eurus. With Eurus having simply shot John with a tranquiliser dart, Sherlock and John stage a scenario where Mycroft will admit Eurus's existence. Mycroft explains that Eurus was the youngest child, 8 years younger than Mycroft