Starting in 1987, three murders were committed on the Western Las Vegas University campus, one of which provided Catherine Willows to investigate a suspect - John Mathers, security guard of the university. Mathers was arrested and convicted. Two years ago he was executed. But the night of his execution another murder with the same M.O. was committed. Eventually, Mathers turned out to be a copycat, responsible only for one murder, and the serial killer got away. And today, the evidence found by Greg Sanders at a fresh crime scene leads Catherine to the conclusion that the killer is back.