A ghost that lives in the city rose gardens will tell him that some of the roses there have suddenly changed hue to black, and will show him where they are. In Dignity Village, an old resident who has passed on and still haunts the place will say that black roses have started popping up around the area, and that they get a weird feeling about them. They'll ask Sherlock to get rid of them, if he can, because ghosts like to ask people for stuff. Overall, it sounds like black roses have appeared a few different place in the city, including the YMCA and various homeless shelters.

After they are planted, Sherlock will come back to find that whatever area he left the trimmings to grow will be over-grown with the same black roses. He might want to do something about that.