The children Julian, Dick and Anne spends a summer holiday at the Kirrin Farm, where there cousin Georgina lives with her dog Tim, and her parents. The tomboyish Georgina is punished for her poor school performance, and her father hires a private teacher.

The four kids, Julian, Dick, Georgina and Anne plus the dog Tim go on a bike-trip without any grownups around, but they are soon followed by a another boy, Richard, who is pursued by kidnappers.