Seven colonies went dark in six months. No distress calls. No bodies.Colonel Dr. Rhea Madrid has been a combat medic, a trauma surgeon and a xenobiologist, which is exactly why Command sends her. She leads a team of thirty-four through the Helios Aperture, the wormhole that links Earth to the Kepler system, to Eidolon-6. It's a Xytherium mine where 247 people disappeared while the station kept filing weekly reports that all operations were nominal.What she finds three hundred meters underground doesn't match any disease she knows. Behind a welded hatch, under the words DON'T SLEEP scratched into the rock in a dozen different hands, eighteen colonists are still alive. Their hearts beat in perfect unison. Something is growing inside them, and it's learning.The organism builds crystal inside its hosts and binds them together, mind to mind. It keeps their memories. It keeps their voices. And it has already found a way off Eidolon-6.On Earth, Madrid's youngest daughter wakes from nightmares begging her not to let them come home. Madrid promised she wouldn't. Keeping that promise will make her the most hated woman in human history. It will also lead her to a weapon that can end the war, if she's willing to kill millions of innocent people along with the enemy and keep her hand on the switch for thirty seconds.Eidolon-6: The Kepler Codex is hard science fiction horror about first contact, and about what one mother will pay to keep a promise.