Police psychologist Sarah Taylor becomes involved with Tony Ramirez as the result of a chance encounter. As their involvement escalates, so do a series of anonymous threats directed at Sarah.

Four volunteers sign up for what initially appears to be a typical paid research study. Quickly, they discover that they have unwittingly become involved with a classified government program that should have been terminated nearly two decades ago. As the study gets underway, the group is presented with a series of questions, and given a finite window of time in which each individual member must submit a unique numerical answer. At first, the participants...