A 17-year-old girl staggers into a health clinic suffering from what appears to be a meth overdose. She thrashes violently as if she's possessed. SNAP! The girl breaks her own arm and shouts something in Latin as the doctor, Jeff Dante, tries to save her. The patient dies before anyone knows what's happened. Megan learns from a nurse that the Latin phrase she uttered means "you're all going to die." The room got cold when the girl came in. The nurse says it felt like evil. The dead girl's name is Rebecca Banks. Megan and Tommy visit with the parents. The father, Caleb, says drugs didn't kill his daughter. The devil did.
There are imprints of crosses on Rebecca's body. Ethan and Curtis are freaked because they weren't there when she was brought in. Megan says the cold air in the morgue brought out the bruises. She brings Kate up to speed on the case since her boss seems to have a lot on her plate with her newfound political aspirations. Tommy has a chat with Rebecca's sister, Chelsea. The girl defied her father by taking her sick sis to the clinic last week. Chelsea says their family lives under a great sin.
Curtis and Ethan find a tooth in the basement of the victim's home. It's a remnant of murders done by a man who killed his three daughters back in 1934. His name is Atticus Aldrich. He's Caleb's grandfather. The guy believed his family was possessed by the devil. The Banks clan slips away from surveillance to hide in a cabin in the woods where Chelsea shows signs of possession. A priest performed an exorcism on Rebecca not too long ago, but refuses to do so for Chelsea now. He's too afraid.
Megan and Tommy burst into the cabin where Caleb is trying to perform an exorcism on his daughter. Chelsea thrashes about violently and stabs herself repeatedly with a crucifix. She punctures her lung. Megan tries to save her. Chelsea says, "Quarter for your jacket, pumpkin. Don't forget." This stops Megan in her tracks. It obviously has some meaning to her. Megan regroups to get Chelsea breathing again. She's rushed to the hospital. Chelsea's sister, Hannah, wants Megan to pray with her. That's not something Megan can do.
Megan reveals why she got so flustered by what Chelsea said at the exorcism. She used to forget her jacket a lot when she was a kid. Her dad said, "Pumpkin, I will give you a quarter for every day that you remember to bring home your jacket. Now go learn something." Tommy wonders how Chelsea could have possibly known that. Megan doesn't have an answer.
Toxicology shows that the girls were suffering from PCP ingestion. It explains the so-called demonic behavior. Megan believes the girls were given PCP involuntarily. The drugs came from Dr. Dante's office. The guy was having a fling with Hannah. Megan realizes the doc's little girlfriend was poisoning her sisters. Hannah holds her dad hostage at gunpoint. She wanted her father's love without her sisters around. Hannah is desperate. She puts the gun under her chin and pulls the trigger. CLICK. The gun misfires. Hannah is safe.
Hannah is arrested for the murder of her sister. Chelsea recovers in the hospital. Megan pays her a visit. The two of them chat about faith and God. Megan asks Chelsea about the comment she made during the exorcism. She doesn't get an answer. Chelsea doesn't remember anything from that day. Megan turns to leave, but she's stopped in her tracks. Chelsea says, "Now go learn something." Megan's face has a look of shock, confusion and perhaps a little fear.