After last week on Elementary, we were left to wonder who was going to reappear in Sherlock’s life from his past. This week on "M", we got a huge peek into what the detective was like before crossing the pond to the United States. "M" was an extremely revealing episode, and one that allowed Sherlock to really become vulnerable and open up to Watson. Not to mention allowing Johnny Lee Miller to showcase his acting skills, which he did beautifully.
When a familiar face reappears in New York, Sherlock is given the opportunity for some much needed revenge. A serial killer that only refers to himself as "M", has made his way to New York after escaping Sherlock’s detective skills in Britain. M killed 37 people, and in a moment of extreme openness, Sherlock tells Watson that M is also responsible for the death of Irene Adler.