The unit heads to Taos, New Mexico where in the span of a week two people were killed, each victim - a male teacher and female clinic physician - with a hole drilled into the exact same spot on the left side of their head. The M.E. is able to determine that the drilling took place pre-mortem and was the cause of death. By the time the unit arrives in Taos, a third victim, a male construction worker, is discovered. One lead is that the physician, Stacy Uqalla, was on the phone with her husband, Michael Uqalla, at the time of her murder, he being able to hear the unsub looking/asking for some specific unnamed item. The unit members discover that all three victims had money issues, and leading out of a subsequent attack and from the nature of the drill holes believe that the attacks have some auditory component to them, with the unsub possibly suffering from humming in the ears, such phenomena which was first attributed within the general population to the Taos area in the early 1990s. The unit members believe the unsub is trying to find the source of the hum, with the victims being anyone who prevents him from doing so or whose help he enlists cannot stop the hum. As such, the unit members have to go on a search for what the unsub believes is the source.
—Huggo