At her uncle's farm in Scotland, young Cathie becomes interested in the Irish farm workers who migrate to Scotland during the summer and are known colloquially as ""paddies"". She is especially intrigued with Jamie O'Flaherty Blake, a stowaway paddy boy whom Cathie at first mistakes for a gremlin. But Jamie is quite real and his friendship with Cathie is the highlight of her summer. As the two children try to locate Jamie's only living relative, a grandfather about whom he has many mixed feelings, their evidence points to Herd, the loyal overseer of the farm. Several henhouse robberies tarnish the good name of the paddies and cause Herd to mistrust his crew until Cathie and Jamie uncover the identity of the thief (a big gray rat) and in so doing reveal Jamie's whereabouts. His reunion with Herd tops off a lifting childlike tale, with a slight mystery filled with the special charm of Scottish-Irish lore.