Nora and Ben's younger sister Birdy loves to keep secrets. She surprises her family more than once: She hides a kitten in her room. She writes a beautiful poem. One day Birdy watches her mother spit into a tube, ready to send it off to find out more about herself and where her family came from. Birdy spits into a tube, too, when no one sees her. But when the test results come back, they are a surprise. Birdy is seemingly not related to Nora and Ben's parents. But if she is adopted, how could that have happened without the children knowing? Nora and Ben must learn when to keep a secret, and who to go to for help - and eventually, how to solve this secret for the entire family.