Why do you love your child? Is it because they're a straight A student, a talented footballer? Or is it simply because they're yours? Sarah and Phil love both their children, James and Lauren. The couple have the same hopes and aspirations as any parent. But their expectations are shattered when they discover that their perfect baby daughter has been born with a flaw; a tiny, but life-changing glitch that is destined to shape her future, and theirs, irrevocably. Over time the family adapt and even thrive. Then one day a blood test casts doubt on the very basis of their family. Lauren is not Phil's child. Suddenly, their precious family is on the brink of destruction. But the truth they face is far more complex and challenging than simple infidelity. It tests their capacity to love, each other and their children, and it raises the question of what makes - and what breaks - a family.