In a small college town in northern California, a lonely young man is working himself to the bone to solve a sixty-year-old problem ... a stranger with a will of iron and eyes the color of ice is searching for someone he can't identify ... and a girl who loves plants is about to grow roots of her own. When Cara Gallagher's parents are transferred overseas again, she's off to spend her senior year of high school living with her sister, a graduate student at the famed McNair University. Cara, a girl with a passion for science and an indifference to people, hopes this move will be her first step in claiming the independence she craves. Cara has her future planned down to the letter: her college, her major, her career. Then she saves Will Mallory's life, and both of their futures are completely rewritten. The last years of Will's life have been spent shifting from one identity to the next, dodging the FBI, and trying desperately to find a way home. But Will's home is forty-four light years away, and to reach it he'll have to outwit the man who's hunting him—and leave behind the only love he's ever known.

It seemed to me, then, that love exists balanced on the edge of a knife, with self-doubt on one side and temptation on the other. And if you succumb to both, there's nothing for you but to be sliced in half, right down the middle of your wanting heart. I was so, so close to the blade of that knife. To save the girl he loves, Will Mallory destroyed his only means of returning to his own world, a decision that lays heavily on Will and Cara as they try to navigate the new life—the human life—they're building together. In the sequel to the acclaimed Caterpillar, a horrifying mistake sends a frantic Cara on a mission to the other side of the country to find James Napolitano, Will's genetic twin. Meanwhile, Will is stalked by a woman from his past, who promises to teach him the control of his Eolian abilities that he's sorely lacking, but at a price that may be too high for he and Cara both. Temptation and danger lurk at every turn as Cara and Will are forced to confront their greatest fear: that the love they've nearly died for may not be enough.