Abaddon's Gate: Expanse, Book 3

For generations the solar system--Mars, the moon, the asteroid belt--was humanity's great frontier. Until now. The alien artefact working through its program under the clouds of Venus has emerged to build a massive structure outside the orbit of Uranus: a gate that leads into a starless dark.

Jim Holden and the crew of the Rocinante are part of a vast flotilla of scientific and military ships going out to examine the artefact. But behind the scenes, a complex plot is unfolding, with the destruction of Holden at its core. As the emissaries of the human race try to find whether the gate is an opportunity or a threat, the greatest danger is the one they brought with them.