Time is running out for four-year-old Sebastian Zair. A rare blood disorder means that a stem-cell transplant is his only hope of surviving past childhood. His mother places her trust in the Pemberton Fertility Centre and a controversial IVF procedure which will allow her to select an embryo that is the same tissue type as Sebastian - to create a saviour sibling. But what she doesn't know is that the sword of Damocles is hanging over the Pemberton. A Nigerian couple, the Opakanjos, have just given birth to twins through IVF, but only one is their biological child. Someone has made a monumental mistake. With a major enquiry under way and pro-life campaigners on the warpath, both families are faced with agonising personal choices as well as the intrusions of an unscrupulous journalist. Will they break under the strain? Will Sebastian survive?