Gyron de London, most powerful—and most hated—industrialist of the year 2190, is warned by a mysterious letter that his doom is due on the 30th March, three weeks hence. Further anonymous letters repeat the message. The frightened tycoon takes every precaution, even to sealing himself in a steel, radiation-proof cube surrounded by armed guards—but death overtakes him on the specified day, exactly as forecast!

Since no one had entered the cube after the industrialist was seen to enter it alive, the police conclude that his death was from natural causes. Famed scientific investigator Adam Quirke is called in by the unsatisfied family, and discovers that de London was the victim of a highly scientific murder. An impossible crime mystery set in the future!