Quick recap
London, 1890. Sherlock Holmes and Dr. Watson arrive just in time to stop Lord Blackwood from sacrificing a young woman. Blackwood is arrested and hanged. Days later he rises from the grave and vows to rule England through fear. Watson, engaged to Mary Morstan, is moving out of 221B but gets pulled back in. Irene Adler, the one person who ever fooled Holmes, returns working for a mystery patron. Holmes breaks down every supernatural trick with science and sleight of hand, and it all ends in a fight on the half-built Tower Bridge. The case closes, but a part stolen from a machine hints at someone bigger behind it.
