What planet are you on? If asked the question, seventeen-year-old Mary Bryan might just tell you Mars or Venus or Neptune. And mean it. Literally. Back on Earth in rural Oklahoma, Mary is a seemingly normal teen living a seemingly normal teenaged life. She rolls her eyes at her annoying parents; wishes secretly to advance her relationship with Zach, her best buddy since first grade, beyond the friend zone; and, except for science with Mr. Walker, has little patience for her small-town high school and its soul-crushing social hierarchy. But after unwittingly transporting herself to another planet during an embarrassing incident in Mrs. Trinson's history class, Mary finds herself both fascinated and terrified by her newfound power. It's a pretty handy thing, after all, to jump to Saturn on a moment's notice—but for that pesky little matter of having no air to breathe. Soon after, Mary's life is thrown into chaos of galactic proportions when her unusual ability draws the attention of an evil force bent on using her to destroy life as we know it on Earth. To make matters worse, her beloved science teacher is in on the scheme. When Zach, too, reveals himself to be more than just a friend—and not in the way she'd hoped for—Mary, no longer certain whom she can trust, must alone find a way to save the world.