According to Matthew

A highly respected priest conspires with his mistress to poison both her husband and his own wife. The story of a socially popular, powerful and highly respected Protestant priest of St Pauls Church in Colombo, and sought after Exorcist, Father Matthew Peries, who in the late 1970's, conspired with his mistress, to murder his wife and the mistress's husband, by poisoning the victims with gradual over doses of insulin. He evaded detection owing to his standing in the community and continued fearlessly with his nefarious activities.