Nancy and her friends George and Bess fly down to Wshington, D.C., to watch some of the world's best tennis players soot for a championship, But the action is hotter off the court when Nancy gets tangled in a bizarre case of mistaken identity.
Nancy bears a striking resemblence to Teresa Montenegro, the rising young star from San Carlos. Then Teresa's boyfirend is kidnapped, and Teresa may be next! In a last, despeate move to outwit the hired guns, Nancy and Teresa trade places. Nancy strides onto center court to play a deadly game of doubles- while a ruthless killer stalks her from the stands.