On holiday with their mother in the Lake District in 1929 four children are allowed to sail over to the nearby island in their boat Swallow and set up camp for a few days. They soon realise this has been the territory of two other girls who sail the Amazon, and the scene is set for serious rivalry.
| Actor | Role |
|---|---|
 Virginia McKennaMrs. Walker | Mrs. Walker |
 Ronald FraserUncle Jim | Uncle Jim |
 Suzanna HamiltonSusan Walker | Susan Walker |
 Simon WestJohn Walker | John Walker |
| SSophie NevilleTitty Walker | Titty Walker |
| SStephen GrendonRoger Walker | Roger Walker |
| KKit SeymourNancy Blackett | Nancy Blackett |
| LLesley BennettPeggy Blackett | Peggy Blackett |
 Brenda BruceMrs Dixon | Mrs Dixon |
 Mike PrattMr Dixon | Mr Dixon |
 John Franklyn-RobbinsYoung Billy | Young Billy |
| JJack WoolgarOld Billy | Old Billy |
| DDavid BlagdenPoliceman | Policeman |