This is the third book of the series. Everyone who knows the main characters is getting used to them being tumbleweeds, so when they announce their plans to travel into the previously visited parallel universes, no one becomes surprised.

Once there, Rita and Gerald first find devastation of epic proportion, but then they visit a civilization that they met during the events of the 1st book. That warlike people had repelled the aggression that had decimated other, less fearsome, civilizations. In order to determine if their own universe can be threatened, they travel to the outer universes that they had never visited yet. There they find the same devastation, but they also find survivors who provide some clues. Little by little, they investigate and eventually discover the identity of an invisible actor who had caused the disasters in many worlds. That leads them back into the world beyond the parallel universes, where they receive a confirmation of their suspicions.

Having enlisted the support of the omnipotent Lord of the world beyond, they return to an outer universe and begin their quest to capture the invisible actor. After many adventures and much effort, they manage to lure the creature into a universe whence it can be returned to the world beyond.