Sherlock is at St.Barts, in one of the labs examining something he found on a crime scene, the case isn't too hard but he wants to be completely sure about his solution, while he does that his assistant sits right across from him, just watching and humming, honestly, they don't know why Sherlock ever hired them, since he seems to work so well by himself but they won't complain since Sherlock pays good money just for them to be there