When police question a man in the disappearance of his pregnant ex-girlfriend and her young son, they discover he has a terrifying capacity for violence. And later, could a seemingly innocuous man searching for a missing girl be a real-life monster?

A missing Colorado woman's roommate claims she'll do anything to help find her, but investigators fear they may have a rare female psychopath on their hands. Later, a killer's angry outbursts could be real, or just an act put on by a skilled manipulator.