Shawn is still unconvinced and goes to the police station for more information. Juliet tells him the usual toxicology report came back clean but they could administer a more specific test if Shawn had something particular in mind. Shawn looks through Gus' index of medications and gets an idea. Later, after a new toxicology report, he tells Gus that the cops found L-Dopa in Agatha's system. It is a Parkinson's medication that, when taken by a person without Parkinson's causes extreme emotional erratic behavior. The girls were not possessed. They were secretly being slipped the medication. Gus asks how Lucy knew about Shawn's childhood and how to speak German. Shawn counters that Lucy logged on to his internet page and that her German was a quote from the movie Run, Lola, Run. He then tells Gus that Westley has Parkinson's and has been on L-Dopa. It looks like Westley, wanting to return to his glory days as exorcist, fed the girls pills to bring on the symptoms, but things got out of hand and Agatha killed herself. Lassiter and Juliet arrest Westley and Gus visits him in jail, where Westley proclaims his innocence. He knows who the culprit is but he can't tell Gus because he heard it in confession. He then tells Gus that a certain proverb has been of great comfort to him lately.
Gus tracks Shawn down at Henry's, telling him about Westley's innocence and his reference to the proverb, which mentions the unfaithful and evil desires. Shawn then puts it all together and, with Gus, Lassiter and Juliet, goes to see Cameron and finds Lucy in his room. Shawn says Lucy wanted Cameron for herself. She drugged Agatha to make her crazy so Cameron would dump her. Unfortunately, the medication made Agatha so unstable, she jumped to her death. When she overheard Westley proclaim Agatha was possessed, Lucy realized she had the perfect thing to throw the cops off the trail. Lucy then breaks down, claiming she never meant to hurt Agatha, as the cops cuff her and lead her away.