Jill has truly terrible PMS: Every month, for four days, she turns into a boy. When she wakes up female from her monthly male interlude, Jill meditates to remove all memories of the previous four days—a feat she accomplishes so successfully she creates Jack, an entirely independent personality for her male self. With the militant help of her fervently anti-Jack mother, Jill tries to lead a normal life. But prom is coming, Jill has a crush and Jack is getting restless. In this dark comedy of sex, gender and sexuality, Jill must come to terms with Jack before her mother’s hostility destroys them both. A yoga-addicted father, a bisexual hottie and a best friend who invents wildly bizarre fashions fill out a cast of quirky, entertaining, well-drawn secondary characters—with the exception of the unfortunate stereotyping of a kitchen worker as the only Hispanic character. Jill and Jack’s story, touched with intrigue, humor and fascinating questions, ends with a conclusion both satisfactory and open-ended. (Fantasy. 14-16)