With imagination and humor AN INVISIBLE SIGN carries a magic all its own. Young Mona idolizes her father, a brilliant mathematician. When he suddenly demonstrates signs of mental illness, Mona begins to obsess about numbers, using them to interpret an unpredictable and threatening world. Now an adult (Jessica Alba), Mona sold superstitions and compulsive behaviors continue to flourish, but a new job as an elementary school math teacher (a position she both relishes and dreads), may force her out of her protective shell.