Unusual activity at sea is a sure sign that Schubert is up to something, and C.W. (at the behest of the Navy) sends the Cetacean to investigate. Mark discovers a crystalline membrane on the sea floor, which can be penetrated to reveal dry land beneath. There, a race of peaceful beings preserve their shrinking, ancient society, and they’re powerless to stop Schubert from enslaving them to mine a valuable crystal indigenous to their island. But as a fellow form of ocean life, Mark may be powerless to stand up to Schubert’s weapons this time.
Cast: Patrick Duffy (Mark Harris), Belinda J. Montgomery (Dr. Elizabeth Merrill), Alan Fudge (C.W. Crawford), Victor Buono (Mr. Schubert), Rene Auberjonois (Mr. Havergal), Tina Lenert (Click One), Flip Reade (Click Two), Whitney Rydbeck (Click Three), Richard Laurance Williams (Jomo), J. Victor Lopez (Chuey), Penelope Willis (Cetacean Crew), Brandyn Artise (Cetacean Crew), Rozelle Gayle (Conrad)
Notes: Director David Moessinger later became a showrunner on numerous popular 1980s TV series, including In The Heat Of The Night, Jake And The Fatman, and Murder, She Wrote; he is the husband of Star Trek: Voyager co-creator Jeri Taylor. Rene Auberjonois was, at this point, one of those “shows up in everything” frequent-flyer guest stars of ’70s series TV; in just three years, he’d land a series regular role on Benson, a decade after which he’d be a regular on a far more coherent SF series, Star Trek: Deep Space Nine.
LogBook entry by Earl Green