The voyages of the Star Ship Enterprise across man's final frontier - space! Its mission: to explore strange new worlds, to seek out new life and civilisations, to go boldly where no man has gone before.

Operations on the planet Janus falter to a halt as one by one the panic-stricken workers are hideously destroyed by an unknown monster. Summoned to assist, Kirk finds he has little time in which to solve the mystery of the silicon spheres they have unearthed before confronting the unique creature whose approach has meant death to so many.