In this series opener, Williams aptly develops this trio of protagonists. The twins, for example, begin the story estranged, having had dramatically different responses to their mother’s chemotherapy and subsequent death. [...] The novel’s latter half rarely slows down, as even the Xenthians’ taking a breather retains the intensity of an active battlefield. [...] Readers may want some answers in the sequel but will surely look forward to more superpowered clashes.