From publisher blurb:
The Grand Stair stretches behind the scenes of the multiverse,
The Doors upon its unfathomably vast span leading the way to gossamer worlds of limitless variety and infinite possibility. While some Doors lead to cozy little realms and quaint pocket realities, others lead to a greater stage where whirling galaxies dance and distant stars twinkle, calling out from the far side of the void.
The Black is a realm of deep space exploration and adventure among the stars, filled with faster-than-light starships, bizarre alien races, and the intrigues of colonial fleets and galactic empires. This starry cosmos is grand and eternal, but things as we know it have changed - the Eidolon and Umbra are in dire flux, and the once-stable laws of time and space are bending, breaking, and letting impossibilities leak in through the cracks. Step in and hire the fastest ship you can, because the next Door is out there, somewhere far, far away.