Leah Lockhart is proudly science-minded and woo-woo averse. But the life she's carefully curated is knocked suddenly off course, first by a destabilizing case of vertigo, and then by an astrology reading that claims she's living way out of line with what was written in her stars.

Incensed, Leah sets off on a mission to prove that astrology is bogus by comparing her life to that of her Star Twins around the world--people born under her exact same map of the stars. But her even deeper guides on a whirlwind journey through Venice, Istanbul, New Orleans, and beyond turn out to be three people already in her orbit: the mother she thinks abandoned her, the father she thinks saved her, and the former boy next door whose love could be the path to her truest self.