Sherlock assists his old friend Rhys in the search for his adult daughter who was abducted from her townhouse by an unknown kidnapper. As Holmes begins searching for clues, Watson is astonished to learn that Rhys is more than just a former colleague of the detective - he used to be Sherlock's drug dealer. As Sherlock struggles to avoid temptation, the case proves hard to crack. Links to a Dominican drug cartel and the missing girl's stepfather seem to lead nowhere. When Rhys begins to get desperate, he starts to wonder if Sherlock's deductive powers require drugs in order to work properly.