An inexplicable phenomenon is sweeping through the city of Urbicand: a cube, discovered during an excavation, lands on the desk of star-urbatect Eugen Robick. Not only is this cube made of an unknown and indestructible material, but it also expands, creating additional cubes at its corners and forming a continuously growing network that even penetrates solid matter. The population is in turmoil, with reactions ranging from religious euphoria to scientific skepticism and military violence. Amidst the general upheaval, the cool-headed planner Robick becomes acquainted with his neighbor Sophie, who runs a brothel and is now establishing so-called meeting places at the network's intersections. However, the struts of the grid continue to expand relentlessly, and life within the network is slowly but surely losing its foundation...