Gyron de London, a powerful industrialist of the year 2190, receives a letter warning him of his doom on the 30th March, three weeks hence. Despite his precautions - being sealed in a guarded, radiation-proof cube - he dies on the specified day, as forecast! When scientific investigator Adam Quirke is called to investigate, he discovers that de London had been the victim of a highly scientific murder - but who was the murderer, and how was this apparently impossible crime committed?