Alpha' s water system needs a rare mineral named Milgonite and scanners detect quantities of it on a barren planet the moon is passing. When Koenig leads a party to the planet to obtain the mineral, the Alphans discover that the rock structures on the planet are sentient and have a need for water, which they intend to take from the Alphans themselves!
Elenco: Martin Landau , Barbara Bain , Catherine Schell , Barry Morse , Tony Anholt , Nick Tate , Prentis Hancock , Zienia Merton , Clifton Jones , Anton Phillips .