Forty thousand years in the past, the last family of Neanderthals roams the earth. Girl, the oldest daughter, is coming of age and her family is determined to travel to the meeting place to find her a mate. But the unforgiving landscape takes its toll, and Girl is left alone to care for Runt, a foundling. As Girl and Runt face the coming winter, Girl realizes she has one chance to save her people, at great cost to herself.

In the present, archaeologist Rosamund Gale works well into her pregnancy, racing to excavate newly found Neanderthal artifacts before her baby arrives. Linked across the ages by the shared experience of birth and early motherhood, and inspired by the recent discovery that many modern humans have inherited DNA from Neanderthals, Girl's story and Rosamund's story examines the often taboo corners of women's lives.