Readers mainly interested in 'stories' are bound to be disappointed by this concise novel: the narrative, as James Blish himself states in the introduction, is minimal. The book's starting point seems simple enough: a machine (the Dirac) enabling instant communication throughout the whole 'human empire' has been built late in the 21st century; those who initially thought that they were its sole inventors are soon concerned with a mysterious person who knows even more about it than they do. These basic ideas serve as the backdrop of a set of provocating speculations about man, time, knowledge, causality, free will, responsibility, history, science and technology, as the three main characters, prompted by the yet untapped potential of the Dirac, explore multiple possibilities. 'The Quincunx of Time' reads like a philosophical dialogue since it's structured around a few, still scenes in which successive (and sometimes contradictory) views are suggested and evaluated through discussion. Each problem is pared down to specific parts, so that all of its angles - from philosophy to psychology, physics, etc. - are considered. Common science-fiction themes, such as the (possible) role of science and technology in the life of man and in the hands of the world leaders, are given original and nuanced interpretations which go a lot further than where extreme resolutions would have gone. Strongly recommended.