The BAU track a serial killer who chooses junkies, prostitutes and the homeless off the streets of Detroit as his victims. The team tracks the serial killer to a pig farm in the wilds of Canada. What they discover confounds them, the killer they profiled turns out to be Mason Turner a quadriplegic. Further investigation uncovers the remains of 89 victims. Mason claims to be a victim himself of his Brother Lucas' violent nature and is forced to watch each of the murders. Once Mason's laptop is confiscated, the team discovers that Mason was experimenting on these victims in the hopes of finding a stem cell link to spinal injury repair. Lucas, still at large with his latest captive, Kelly awaits instruction from his brother. Kelly manipulates Lucas' childlike demeanor and in the process confiscates his cell phone allowing the team to trace the signal to her location in the woods. Kelly is rescued and Lucas is killed in the confrontation, while back at the farm, William kills Mason, avenging the murder of his sister. The Reaper pays Hotch a visit in the end.