If you save someone's life, you become responsible for them. When Anna receives a letter from Adam, thanking her for saving his son Max's life with a bone-marrow donation, it's the first positive thing that's happened to her for a long time. Grief-stricken at the recent loss of her baby, she's failed to give life in the past. Now this four-year-old boy is alive and healthy because of her: it's a heady realisation. Anna is desperate to get to know Max, yet terrified of how responsible she feels for him. So she decides not to tell anyone about him or that she's arranged to meet his father. Soon she is immersed in a complicated double life, spending half the week with her husband, who believes her to be filming out of town, and the other half with Adam and Max. But Anna has lied to Adam about who she is. And she's lied about her marriage. And soon these lies will catch up with her...