Ally by Karen Traviss

The worlds orbiting Cavanagh's Star are in turmoil.

Civil war on Umeh—ignited by outsiders—threatens to annihilate the teeming masses of a grossly overpopulated planet. On Bezer'ej, the handful of native aquatic creatures who survived extermination must take extraordinary and terrible steps to ensure the future of their kind . . .

And the interlopers from a distant planet called Earth can only watch the chaos they helped, in part, to create—knowing their home world will be next to suffer.

The day of reckoning is rapidly approaching when the powerful Eqbas will remake the Earth at the expense of its dominant species. And Shan Frankland—once a police officer, once human, now something much more—must decide where her loyalties truly lie: among the gethes, on a planet she once called home, or here, where a dying species presents her with a new and unexpected crisis.