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.
After his stint with Mi6, Sherlock returned from London with Kitty (Ophelia Lovibond), his latest apprentice. She and Joan clashed, then bonded. Kitty left after confronting and disfiguring her rapist, fearful of possible arrest.