"Charlie Tannehill and her twin sister, Maggie, are just eight years old when an unfortunate scientific discovery upends their world--and the world order. The revelation? Extinction, encoded in every creature's DNA. The expiration date for humans? Only four generations away. A decade later, unsure of what tomorrow holds, Charlie and Maggie enroll as counselors in a government-run human-husbandry program. By offering cash rewards for reproduction, they hope to forestall humanity's decline and discover a genetic mutation that might defeat it. While Charlie struggles with the ethical implications of the work, Maggie makes unspeakable sacrifices to improve her odds of success--but such unchecked ambition could come at a greater cost than even she realizes. Torn between her own morality, her love for her sister, and the pressures of a vanishing civilization, Charlie must search deep within to decide what she's willing to sacrifice--for herself, for Maggie, and for society--to salvage hope for the whole of humankind" -- Provided by publisher.