Complex sentence: The encounter ends with the man snarling in anger and going away, but that is not the last that Watson sees of him, for a short time later, the man comes to Watson's study to apologize for his earlier behaviour.
Split into simpler sentences: The encounter ends with the man snarling in anger and going away. However, that is not the last that Watson sees of him, for a short time later, the man comes to Watson's study to apologize for his earlier behaviour.