2 boys and 2 girls pack tent etc. on their bikes and go camping at the beach. They bring a German Shepherd. A boy joins them next morning and the "wrong" boy gets kidnapped.
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. Based on Enid Blytons "Five get into trouble," - and that's just what they do!—jpjensen