The novel “Dichronauts” by Greg Egan was published for the first time in 2017.

Seth and Theo live in a symbiosis that allows them to combine their physical abilities to live and work in their world where there are two spacel and two time dimensions. Seth has mobility and sees forwards and backwards whereas Theo, who lives in Seth’s skull, sees what lies to his left and right. Together they can scout the territory and let others know about the safe routes to travel.

Because of the conformation of the world in which the Seth’s and Theo’s peoples live, they live a nomadic life, periodically moving their cities to keep them in habitable areas. During a survey expedition, the two of them encounter something never seen before, a fissure in the surface of the world so wide that nobody can see how far it gets. The next migration will be blocked unless someone explores a territory different from the rest of the known world.