Which clues found at saxecoburg square lead to Holmes's solution of the mystery?

Holmes solved the mystery at Saxe-Coburg Square by noticing the discrepancy in the address written on the letter and the address where the man claimed to have been. He also deduced that the man must have come face-to-face with a dangerous adversary by observing the injury on his hand and the cigar ash on his coat. Holmes concluded that the man had visited a high-risk establishment, which ultimately led to the resolution of the case.