A secret shared

"Nora and Ben's younger sister Birdy loves to keep secrets...One day Birdy watches her mother spit into a tube, ready to send it off to find out more about herself . . . 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?"--Provided by publisher.