After discovering his ability to walk between alternate dimensions, Joey Harker is thrust into a high-stakes conflict between the forces of science and magic that threaten the stability of the entire multiverse. Joey, an unremarkable teenager who struggles with basic navigation, finds himself recruited by an interdimensional organization composed of alternate versions of himself. He must navigate the complex geography of the 'Altiverse' while resisting the machinations of powerful magic-wielders, Lord Dogknife and Lady Indigo. The narrative unfolds through a fast-paced, third-person perspective that emphasizes the physical and logical challenges of traversing disparate realities. As Joey undergoes training, he learns that his survival depends on his ability to coordinate with his own counterparts to maintain the precarious balance of power.

Critics and readers have noted the book's success in blending science fiction and fantasy elements into a cohesive, fast-paced narrative. The premise of an army composed of alternate versions of a single protagonist is frequently highlighted as a creative hook that drives the story forward. While some reviewers have pointed to minor inconsistencies in the internal logic of the world-building, these are often balanced by the vividness of the settings and the imaginative character designs. The work is widely regarded as an accessible entry point for younger readers interested in complex, multidimensional concepts. Overall, the reception reflects a consensus that the collaboration between Gaiman and Reaves produces a compelling, action-oriented experience.