Twelve-year-old Shari Tucker isn't the happiest girl on the planet. She doesn't have many friends, has no brothers or sisters to play with, and is pretty lonely. But then something strange happens: a cute boy, Robby, actually asks if he can hang out with her!
But that's just the beginning. After Robby talks to her, Shari suddenly gains a new best friend in Holly, and more than one boy starts talking to her. Suddenly, she's something she always wanted to be: popular! But then, she is invited to a nerdy girl's birthday party, a move that really doesn't work well for her new popular-girl image. Shari reluctantly goes-and then comes up with the idea to pretend to sprain her ankle so she can go home.
Once at home, though, she receives the shock of her life: her family is moving! Her parents secretly adopted a baby girl but accidentally got one from Spain, and their doctor advises the entire family to move to Spain to help the baby adjust.
Shari thinks this whole baby thing is pretty suspicious. With the help of her new friends, Shari determines to discover the truth about her new baby sister.