Marco's Millions

In William Sleator's 'Marco's Millions,' twelve-year-old Marco, driven by his love for travel and his younger sister Lilly's psychic abilities, finds himself on an extraordinary interdimensional adventure. When Lilly senses strange lights in their basement, they uncover a portal to another universe inhabited by insect-like creatures. These beings believe Marco and Lilly are destined to save their dimension, and by extension Earth, from a powerful, destructive singularity. The catch: time moves differently, meaning days spent in the other dimension equate to weeks on Earth. Marco must make a difficult choice, lying to his parents about a vacation to undertake a perilous mission. This prequel to 'The Boxes' is a fast-paced science fiction novel exploring themes of bravery, sibling bonds, and the weight of responsibility, suitable for readers aged 9-12.

Twelve-year-old Marco's love for travel and for his younger sister Lilly, who has psychic powers, leads him to journey to other universes, gaining the ability to go wherever he wishes without growing old.