With their cruel stepfather in pursuit, two British runaways Finn Dove and his sister Derval decide to go to Ireland to the safety of their Granny O'Flaherty.

After suffering continual torment from their cruel stepfather, Tobias Cromwell, thirteen-year-old Finn Dove and his seven-year-old sister Derval plot to run away from their home in Liverpool to the Galway, Ireland farm of their kindly grandmother, Mary Magdalene St. Bridget O'Flaherty. Unknown to the children, they are the beneficiaries of a trust set up by Mary's recently deceased husband, with each child to inherit ten thousand dollars. The trust further states that in the event of their deaths, the money would pass on to their uncle, John Cyril Dove, a fading vaudeville actor performing under the name of Hawk Dove. When the impoverished Hawk is fired from a nightclub for his uncontrollable temper, he decides to do away with his nephew and niece to claim the inheritance. In Ireland, the feisty Mary confronts Judge Liffy, demanding that he assist her in becoming Finn and Derval's legal guardian. Back in Liverpool, Hawk disguises himself as solicitor Maxwell Perdon and approaches Tobias with the proposal that he could help Tobias gain access to the children's inheritance. Although furious to discover the children have gone missing from Tobias' house, Hawk discovers a geography book with the map of Ireland torn out and realizes their destination. Tobias and Hawk report the children's disappearance to the police, who soon contact the Irish police to watch for them. Meanwhile, Finn and Derval, with only pennies between them, go to the pier and, mingling with a large family, stow away on a steamer ship bound for Dublin. Arriving the next morning, the children pass easily through customs when the agent heartily welcomes them to Ireland on St. Patrick's Day. That same afternoon, Tobias flies to Dublin and is met by Irish detective inspector Michael Roark, who has been informed by the British police of the children's disappearance. Tobias implies that Mary has kidnapped the children and when questioned by reporters, announces a reward for information on Finn and Derval. Arriving on the same plane with Tobias is Hawk, now disguised as British Chief Inspector Wolcott, who informs Roark that he must be included in the search for the Doves. Unaware that their pictures and Tobias' offer have been splashed across the television news, Finn and Derval trail hungrily through Dublin's open markets, unable to afford food. Under the watchful eye of a shifty local, Mickser, Finn boldly snatches a meat pie. The children are spotted by a policeman and chased through the streets into a shopping center where they are amazed to see themselves on television. Overhearing a news report about their disappearance, Finn and Derval learn that Tobias has followed them to Ireland. Evading the policeman, the children seek refuge in a synagogue, where a friendly rabbi helps disguise them so they can escape safely. The children are then swept up into an exuberant St. Patrick's Day parade, which takes them to the edge of the city. From there, the pair begins the long walk to Galway but are soon offered a ride on a horse-drawn cart, driven by Mickser, who has recognized them. When Mickser stops at a local pub for a quick pint, Derval panics when he reveals he has a tattoo, which reminds her of their wicked uncle Hawk, known for the hawk tattoo on his wrist. Observing Mickser using the pub's telephone, Finn and Derval conclude he is Hawk in disguise and, taking a local constable's bicycle, flee. Roark receives the report made by Mickser of the children's location and tells "Wolcott" that as there are only two routes from there into Galway, he plans to intercept them. As darkness descends, the hungry and exhausted Finn and Derval spend the night in a graveyard so they will be safe. Before dawn, however, the children are startled by the arrival of a van and several men arranging to transport illegal liquor into Galway. Although realizing Mickser is the van's driver, Finn urges Derval to hide in the van to reach Galway quickly. On the drive, Mickser picks up Constable Flynn, who laments the theft of his bicycle. At dawn, Roark's roadblock stops the van and the impatient Hawk, still posing as Wolcott, angrily questions Mickser, who demands the reward before relating information about Finn and Derval. Inside the van, Finn hastily covers his and Derval's faces with coal dust and, finding scissors, cuts his sister's hair and places his clothes on her while putting on her small dress. When "Wolcott" demands an inspection of the truck the now unrecognizable children are able to escape. Discovering Flynn's bicycle and scissors, however, Hawk realizes what has occurred and he and the policeman pursue the children into a wool factory. After a grueling, fruitless chase, Hawk returns to Roark to announce he is turning the case over to him. Suspicious of "Wolcott's" abrupt departure, Roark requests information on the inspector. Meanwhile, Hawk makes another transformation into newspaper reporter Miss Heather Marblestone. On the road, Finn and Derval's attempt to steal a donkey results in their being attacked by several children, part of a group of traveling gypsy tinkers led by Powder O'Ryan and his daughter Sheila. Finn apologizes for attempting to steal the donkey, but Powder, who has also recognized the pair, assures them he will help. The next day in a pub, however, when Powder hears locals speculating that the reward for the Doves has likely increased, he telephones the police, who inform Roark. Hawk, as Miss Marblestone, follows the police to the village and overhearing an angry Sheila chastising her father for giving in to greed, offers to help. Just as Hawk spirits Finn and Derval away, Roark, Tobias and the police arrive at the pub. Roark reveals he has learned that Hawk was masquerading as the real detective Wolcott and suspects he is after the inheritance, putting the children in grave danger. Meanwhile, Hawk drives the children to a nearby castle on a hill overlooking a large lake, into which he attempts to push them. Spotting the tattoo on his wrist, the children recognize Hawk and manage to escape. On the edge of despair, the children are about to give up when they finally reach Mary's farm, where they are spotted by hands Paddy and Seamus, who take them to the delighted Mary. As Roark, Tobias and the police descend upon Mary in search of the children, she promises her grandchildren that she and the neighbors will protect them. When the police present a warrant to search Mary's house, Finn and Derval flee with a kindly farmer to the barn, unaware that it is Hawk, again in disguise. Shocked when Hawk tries to attack them with an axe, Finn then offers his uncle the entire inheritance, declaring that living with Mary would provide them all they have ever wanted. Unable to harm the children, Hawk returns them to the house, but is upset when Roark arrests him for impersonating a detective. Summoned by Mary, Judge Liffy arrives and after questioning Finn and Derval, decides they would be happiest with Mary, forcing Tobias to concede defeat. Discovering that Hawk has tied up a policeman and fled in his uniform, everyone laughs and the children settle down in their new home.