The World Next Door.
Engineered by the mysterious Hypotheticals to support human life, it's connected to Earth by way of the Arch that towers hundreds of miles over the Indian ocean. Humans are colonizing this new world - and, predictably, exploiting its resources, chiefly large deposits of oil in the western deserts of the continent of Equatoria.
Lise Adams is a young woman attempting to uncover the mystery of her father's disappearance ten years ago. Turk Findley is an ex-sailor and sometime drifter. They come together when an infall of cometary dust seeds the planet with tiny Hypothetical machines.
Now Lise, Turk, a Martian woman, and a boy who has been engineered to communicate with the Hypotheticals, are drawn to a place in the desert where this seemingly hospitable world has become suddenly very alien indeed - and the nature of time is being once again twisted by entities unknown.