CLOSE TO CRITICAL. New York: Ballantine Books, . Small octavo, pictorial wrappers. First edition. Ballantine Books U2215. "Humans attempt to contact the alien inhabitants of the extremely inhospitable heavy gravity planet Tenebra. A scrupulously scientific adventure which hews closely to the author's earlier success, MISSION OF GRAVITY. The result is not quite as effective, though." - Pringle, The Ultimate Guide to Science Fiction, second edition (1995), p. 71. Anatomy of Wonder (2004) II-257. A fine copy. (#87812).
"First Printing, July, 1964" on copyright page.