As the inhabitants of Pern finally near their longtime goal of ridding their world of the hazard of Thread, they regain contact with the shipfish, the dolphins that accompanied the earliest human settlers on the planet. T'lion, a young dragonrider, and Readis, a boy from a fishing village, are instrumental in rebuilding the ancient partnership between humans and dolphins in preparation for the spread of humanity over the remaining wildernesses of Pern.  

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