When 17-year-old Rosie's mother, Trudie, dies from Huntington's Disease, Rosie's pain is intensified by the knowledge that she has a 50 percent chance of inheriting the crippling disease herself. Only when Rosie tells her mother's best friend, "Aunt Sarah," that she is going to test for the disease does Sarah, a midwife, reveal that Trudie wasn't her real mother after all. Rosie was swapped at birth with a sickly baby who was destined to die.
Devastated, Rosie decides to trace her real mother, joining her ex-boyfriend on his gap year travels, to find her birth mother in California. But all does not go as planned. As Rosie discovers yet more of her family's deeply buried secrets and lies, she is left with an agonizing decision of her own, one which will be the most heartbreaking and far-reaching of all.