Sherlock Holmes' brother, portrayed by Richard E. Grant. He has a history of opium addiction, which was forcibly induced by Professor Moriarty during their younger years. His appearance highlights the long-standing personal threat Moriarty posed to the Holmes family.
Moriarty has a long-standing harmful influence over Mycroft.
The plot states that Moriarty forced Mycroft into opium addiction when the Holmes brothers were young.
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