Costanzo´s La Solitude dei Numeri Primi is a screen adaptation of best-selling novel of Paolo Giordano. As Giordano notes in his book, prime numbers can only divided by one or themselves, and the two principle characters in his story reflect a similar singularity in the loneliness. As a child, Alice was forced by her father to join him for a skiing trip where she broke her leg, causing her to walk with a limp for the rest of her life. Meanwhile, Mattia had to attend a birthday party with his developmentally disabled sister, Michela, and when he turned his back on her for a moment, she disappeared. The physical and emotional scars of these events haunt Alice and Mattia through much of their lives, while she is clearly attracted to him and their lives cross paths on a regular basis, various circumstances prevent them from coming together as a couple, as Alice becomes an assistant to a successful photographer and Mattia goes on to a distinguished career as a mathematician.