Don and the team investigate a series of murders where all the victims are men that sleep with prostitutes. DNA evidence reveals that the killer is a woman and that she has a rare blood condition. A database search doesn't produce any leads until Amita thinks to search for partial matches with similar genetic variables; if the killer is not in the system maybe someone in her family is. The search leads to Melanie Bailey the sister of a prostitute who has been beaten and left for dead. The team suspects that she's not working alone. When they track her down in a hotel bar on the hunt for her next victim she refuses to give up her partner. After David and Colby review surveillance footage and talk to the bartender they figure out who Melanie and her partner have targeted. Now they have to get him before he becomes their next victim.
