A prime number can only be divided by itself or one-- Alice and Mattia are both misfits who seem destined to be alone. Haunted by childhood tragedies that mark their lives, the cannot reach out to anyone else. When Alice and Mattia meet as teenagers, they recognize each other a kindred, damaged spirit. But the mathematically gifted Mattia accepts a research position thousands of miles away, and the two are forced to separate. Then a chance occurences reunites them, forcing a lifetime of concealed emotion to the surface.