Dr. Hawes has aided Sherlock and Joan with their cases. He and Sherlock are regular chess partners. After Hawes was almost killed by an explosion in the morgue, he got addicted to drugs, and Sherlock encouraged him to get help.
Holmes: Why do you suppose you hate your job so much? Watson: I don't hate my job. Holmes: You have two alarm clocks. No one with two alarm clocks loves their job. Two alarm clocks mean it's a chore for you to get up in the morning.
Watson: How do you do it, guess things? Sherlock: I observe and then I deduce. Watson: How did you know I was a doctor, you said you could tell from my hands. Sherlock: Hand, singular. It was soft no calluses. Watson: How did you know my father had an affair? Sherlock: Google. Not everything is deducible.