Two friends, a poet and a mathematician (who is described as the author of a study on "the theorem which Fermat did not write in the margin of a page of Diophantus") arrive at an abandoned house in the poet's hometown. The poet explains that the house is a labyrinth and that his owner was killed in it many years ago. He tells his friend the story of the man and his death, which remains a mystery. The mathematician after a couple of days of thought meets his friend again and explains to him the correct solution. Passing references are made to set theory and the description of a straight line as the arc of an infinite circle, although neither figures prominently in the plot.