In a parallel present San Francisco, Natalia Peña works as a hotel maid, practices martial arts, and cares for her eleven-year-old brother, Calvino. In this version of our world, all children start to "wane" when they reach Cal's age; by their teen years, they've lost their ability to feel emotion. But Cal isn't waning. When a mysterious corporation kidnaps him for testing, Natalia's reaction surprises her: she's crushed, and she'll do anything to save her brother from their experiments. But the road to his rescue leads her into the path of a dashing but troubled billionaire's son, a cadre of killers, and, eventually, the shocking truth about waning.