Plot Synopsis

DIABOLICAL is a one-hour docuseries that tells the stories of shockingly devious masterminds, who use their wits and wiles to manipulate others, seduce them, and then try to get away with murder. On Monday, January 1, 2018 at 3pm ET/PT, Investigation Discovery premiered a single sneak-peek episode of DIABOLICAL, but the cable channel had no other episodes on its schedule at that time. In the sneak peek, "Mistress Roulette," Dr. Adam Frasch is living large with a wife and baby. His practice is booming, he loves to spend money on houses, exotic cars, and exotic dancers who become mistresses. Ultimately, the doctor discovers that sowing deceit and jealousy reaps serious consequences. Ten weeks later -- on Thursday, March 15 -- DIABOLICAL had its official series premiere, as Investigation Discovery debuted the "Lying for Love" episode. After a rocky first marriage, Tim Koile has a new bride and a fresh lease on life. But when temptress Cathy Cousin moves next door, the married woman wraps the devoted father around her finger, and has him satisfy her every whim -- no matter how diabolical.

On Tuesday, May 21, 2019 at 9pm ET/PT, Investigation Discovery premiered the second season of DIABOLICAL. In the season opener, "Mother of All Lies," Detective Scott Sanderson finds himself solving one of the strangest cases of his career in 2015. At its center are a newborn and her missing mother. Before long he'll uncover a diabolical scheme that will destroy the lives of everyone it touches.

Season 3 of DIABOLICAL premiered on Tuesday, March 10, 2020 at 9pm ET/PT on Investigation Discovery. In the season opener, "Daddy's Little Nightmare," the city of Federal Heights, Colorado is filled with fear in 2017 when 69-year-old veteran Bill Mussack is reported missing gone without a trace. Police act fast to uncover a diabolical killer with a heinous plot, before this malicious murderer strikes again.
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On Tuesday, May 12, 2020 at 8pm ET/PT, Investigation Discovery premiered "Evil Sister Act," the season finale of DIABOLICAL. When Samuel Johnson Jr. suddenly vanishes, San Antonio investigators find themselves face-to-face with two sisters who know something. Through a series of interrogations, they reveal an elaborate murder plot meticulously engineered by a puppeteer.