With imagination and humour An Invisible Sign carries a magic all its own. Young Mona idolises 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's old superstitions and compulsive behaviours continue to flourish, but a new job as an elementary school maths teacher (a position she both relishes and dreads), may force her out of her protective shell.