The Rising Tide

The Earth has died.
Five years after the Collapse, the remnants of humanity travel through the stars inside Forever: a living, ever-evolving, self-contained generation ship.
When Eddy Tremaine and Andrissa "Andy" Hammond find a hidden world-within-a-world under the mountains, the discovery triggers a chain of events that could fundamentally alter or extinguish life as they know it, culminate in the takeover of the world mind, and end free will for humankind.

Eddy, Andy, and a handful of other unlikely heroes must find the courage and ingenuity to stand against the rising tide. Otherwise they might be living through the end days of human history.
"Quality, innovative worldbuilding grounds this volume in the "Liminal Sky" series. Fans of The Expanse will find plenty to enjoy here as different groups with widely varying goals and beliefs come together in a struggle to survive the vastness of space and one another." -Library Journal