The Expanse. Book 3. The Gate of Abaddon

The third book of the bestselling series, which has sold ten million copies, won the Hugo Award, and served as the basis for a TV series that ran for six seasons.
The protomolecule is an extraterrestrial substance capable of subjugating and transforming organic matter. Billions of years ago, it was cast into the Solar System with the aim of reshaping the Earth's biosphere, which at the time consisted of single-celled organisms. But it never reached Earth, getting stuck on a moon of Saturn, where it was only recently discovered by a Martian expedition.
The protomolecule killed thousands on Eros and nearly destroyed the entire population of Mars, and then, hiding under the clouds of Venus, spent almost a year building something. And now the artifact it created has appeared in orbit around Uranus. It is a gigantic Ring, a portal to starless darkness.
The Rocinante, captained by Holden, is part of a large fleet of ships sent to investigate the mysterious object. What does the Ring promise humanity — the greatest chance or a deadly threat?
But while scientists, military personnel, and journalists are trying to find an answer to this question, a much more serious danger looms over Holden and his team.