From the back cover:
DISTANT WORLDS AWAIT
The discovery of the protomolecule changed everything but it was only with the opening of the Ring that humanity began to understand the power and scope of the alien technology. A massive construct out near the orbit of Uranus, the Ring is a portal into a strange non-space known as “the slow zone.” Centered on an ancient alien station, it connects to more than a thousand other portals leading to a thousand different star systems, each with one or more worlds shaped by the ancient aliens who created the protomolecule. Now the aliens are long gone, and the unlocking of the ring gates has opened vast frontiers for human settlement and exploration.
Beyond the Ring advances the timeline of The Expanse RPG to the fourth novel in the series, Cibola Burn, and details the slow zone, Medina Station, travel through the ring gates, and some of the many systems found beyond them, along with tools for Game Masters to design their own systems for characters to explore.