Crystal Water, Sudden Death
S01E07 - Airdate: 1977-11-22
Runtime: 60 min
The Cetacean finds an underwater forcefield, which shelters a race of air-breathers with a strange clicking language. Mr. Schubert forces the Clicks to mine crystals for him, but taking the crystals will cause the field to collapse and kill them all unless Mark can intervene.
Episode details and rating from TVmaze.