This is a sequel to Dive to Danger (1964) in which Stein Holm and his group of frogmen, including his sister Ellen, a ""froggirl,"" are summoned when a leak in a Great Lake Dam eventually results in a catastrophic flooding of the valley below. Trees and houses float, and Stein and his associates swim in and out of them salvaging humans and animals. When a second dam is imperilled, they are engaged on a still more dangerous mission-- deep water drilling. Once again one can only commend the efficient technical detail at hand; the characters are totally concealed in their suits; the dialogue, while thin-lipped, is lifeless; and the story rarely surfaces. It's rather more of a documentary.