Zapper and his team leave Saturn on a do-or-die mission to conquer Earth and its inhabitants. If they fail, they face losing their planet and being banished to the raging Sun, where the evil Fire Blazers live. After a narrow escape from dangerous attacks on their way to Earth, Zapper is adopted into the Gurble household, where Sally and her dog Scruff become suspicious of Zapper. Things take a different turn, and the whole mission is threatened. Zapper is the first of two novels, followed by a sequel called The Revenge of the Fire Blazers.