The CSIs stumble upon a grisly multiple murder related to a girl who has been through an exorcism. The victims are parents of Amy, a 12-year-old wild child, and they had attempted to rein her in when they discovered that she was in a relationship with a 23-year-old man. Eventually the parents became convinced that their daughter was possessed, and sought the help of a fly-by-night exorcist. Unfortunately for them, the exorcism failed, and they end up murdered. Amy is still missing.
While the police search for Amy, the CSIs must figure out who committed the killings. At first they believe the older boyfriend was involved in child porn, and he murdered the parents to get to Amy. But Amy is soon found with her boyfriend, and she's placed with child services. As the evidence begins to point to an even more shocking conclusion, the exorcist takes matters into his own hands. He knows the truth: that Amy committed the murders of her own volition. He hunts Amy down, and throws her to her death at the Child Protective Services facility.
Meanwhile, Sara works a case with a newbie CSI named Ronnie Lake. Their vic is a homeless man who died of a cardiac arrest, due to dehydration. But Sara notes a complication: handcuff marks on the man, which lead her to believe a cop may be responsible for the death. It turns out that the homeless man had punched a police officer, who decided not to bring the man in. The cop knew the man had only started the fight to go to jail where there's food and water. Sara wishes the cop had taken him in after all.