Grace and Dan Arden are in their forties and have been on the IVF treadmill since the day they got married. Six attempts have yielded no results, and with each failure a little piece of their hope dies. Priya Laghari and her husband Nick Archer are being treated at the same fertility clinic, and while they don’t face the same time pressure as the Ardens, the younger couple have their own problems. On the same day that Priya is booked for her next IVF cycle, Grace goes in for her final, last-chance embryo transfer. Two weeks later, both women get their results. A year on, angry and heartbroken, one of the women learns her embryo was implanted in the other’s uterus and must make a devastating choice: live a childless life knowing her son is being raised by strangers or seek custody of a baby who has been nurtured and loved by another couple.