Maddie Angler is a failed art history graduate student living in Amherst, Massachusetts. When her boyfriend of five years, a brilliant physics doctorate student named Alvin, disappears one February evening, Maddie's world abruptly falls apart. To help cope with matters, she takes over as caretaker for Alvin's mentally challenged brother, Randy.
After spending a year trying to reconcile with Alvin's loss, and discovering hints of his infidelity, she is on the verge of accepting the inevitable—that Alvin killed himself. But when she is confronted by Alvin's old professor, Dr. Keats, she learns some disturbing news: Alvin is very much alive. He's just not in this world.
Despite her attempts to deny Dr. Keats's claims, Maddie is taken against her will across worlds and given the opportunity to speak to Alvin one last time. In the process, she discovers that she is merely a small player in quite a large universe, and that that her own world—in fact, her own self—is but a variation on a theme. If she has any hopes of returning home alive, she must learn to look into the mirror and face her true self, in all its many forms, or else lose those she loves the most.