O'Brien was an important contributor to the type of fantasy tale exemplified by Poe and Bierce. His finest and best known story, "The Diamond Lens," is included in this collection. O'Brien's "importance rests on a handful of brilliantly original sf tales, which were influential not only on subsequent sf but also on the development of the short-story genre." - Clute and Nicholls (eds), The Encyclopedia of Science Fiction