Continuity mistake: In the beginning, Joan and Sherlock are chatting in the living room. Joan has her hands in her lap, then she is resting her right arm on the arm of the chair.
Continuity mistake: In the prison, Captain Gregson takes five shoes out of a suitcase, but when it comes time to leave, Gregson doesn't put the shoes back in the suitcase because they are already there, and he could not have done it without us seeing it.
Chosen answer: M broke into the brownstone and left a note. Holmes deduced he was staying at a high-class hotel from the soap scent on the note, and gave a picture from a hidden camera to his "irregulars" on the street to stake out hotels. One of them saw him, so Holmes followed him to his next intended victim and knocked him unconscious with a baton.
Sierra1 ★