Patrick Simson was a minister in the parish of Renfrew. He was an experienced clergyman, aged sixty nine years old. He would have lived through some of the more intense witch hunts of the past, and would have had strong memories of the religious strife experienced in Scotland during the preceding decades. Like Andrew Turner from Erskine, he too was present during many of Christian Shaw's episodes of physical torment and spiritual challenge. Simson testified that he was in the room when Margaret Lang had challenged Christian Shaw in her bedroom at Bargarran House. Simson confirmed that the young girl had suffered an extremely violent fit, and that Margaret Lang had subsequently declared "Lord God bless thee and ding the devil out of thee."

Simson confirmed that when Lang left the room, Christian Shaw revealed that a charm had made her unable to accuse the midwife to her face, but now that Lang had left the room, and she had been made aware of the charm's presence, she could see to its disposal and reaffirm her accusation.