"DEVIL YOU KNOW" delves into the secret lives of men and women who masquerade as law-abiding citizens but, behind the charade, are hiding deadly intentions from their loved ones. As each story unfolds, family and friends give first-hand accounts of the unimaginable betrayal that left them in the dark. These harrowing personal testimonials take viewers on a twisted journey as our witnesses wrestle with the demons and devils they have come to know all too well. / (Source: Investigation Discovery)