Synopsis by Hal Erickson
$75 million in stolen diamonds is hidden somewhere on the ocean floor. Only Frederick Hoffman (Jeremy Slate) knows the actual whereabouts of the gems, and Hoffman is currently the prisoner of sadistic master criminal George Berlinger (Fritz Weaver). The IMF must recover the diamonds before Hoffman cracks under Berlinger's torture--and to accomplish this, Phelps and Casey must convince Berlinger that they know what he wants to know. The underwater scenes were filmed on location at Marineland of the Pacific. Wrtten by Arthur Weiss, "Underwater" was first telecast on November 6, 1971.