In the Lost Tales of Kalhar there is a creation cycle myth that tells of a “World Tree”. For many years only known in oblique references, Arc historians hypothesised a connection with Norse mythology across a vast gulf of time and space, but when the text in question was finally found it proved to be a cautionary tale more relevant to our future than our past.

The Gommen home trees were a cheap, efficient solution to the problem of sheltering a population rapidly spreading into an uninhabited wilderness – a single genetically engineered seed would grow, within mere days, into a comfortable dwelling for three, then die, wooden walls and floors becoming harder and more durable than stone. The seeds were sterile, unable to germinate on their own. Unable, that is, until a particularly hardy ground shrub managed to cross-pollinate with a home tree while it was still growing.

A single flowering of ornate gazebos and a stiff breeze was all it took to spread the hybrid across tens of miles, which soon turned into hundreds then thousands of miles. Within a year every continent was choked and overgrown with second bathrooms and third bedrooms – here and there even the occasional conservatory or powder room – all twisted and tangled with branches and corridors and tied together into the great World Tree.