WHEN SARA STANLEY AND JO PITTS MEET, FELIX KING DOES a double take. "You two could be twins!" he says. But Felix's innocent observation brings a mischievous glint to Sara's eyes. Desperate to escape the clutches of her overbearing Aunt Hetty, Sara convinces Jo, a streetwise orphan, to switch places with her. Meanwhile, Sara gets Gus Pike to take her to the mainland — leaving a confused Hetty to deal with the uncontrollable new Sara Stanley. But the plan backfires. When Gus suddenly disappears, Sara finds herself face-to-face with Jo Pitts' dangerous past.