Adam Bell is a glum, disheveled history professor, who seems disinterested even in his beautiful girlfriend Mary. Watching a movie on the recommendation of a colleague, Adam spots his double, a bit-part actor named Anthony Clair, and decides to track him down. The identical men meet and their lives become bizarrely and irrevocably intertwined. Gyllenhaal is transfixing as both Adam and Anthony, provoking empathy as well as disapproval while embodying two distinct personas.