After a health scare, Lou is forced to consider that the time to have a family is running out. The problem is: even though her eggs are viable, she and her partner don't have enough money for the necessary fertility treatment. Meanwhile, up in Yorkshire, Cath, a little older than Lou, is longing to start her own family with her husband, Rich. But she's recovering from cancer, and as a result of chemotherapy is infertile.

Lou and Cath, brought together by a fertility clinic, end up egg-sharing - a process where a woman who has good eggs can donate them to another who needs them, in return for free IVF. As both women simultaneously try to conceive, with the same woman's eggs, the novel follows their parallel journeys to create a family - and as the foetuses grow, so does the novel.