Australia

Sand, surf and adventure with our four intrepid youngsters!
Johnny, Sue and Ann, together with their American friend, Pete, spend most of their summer days surfing and playing around In boats. But a strange trawler with a mass of radio equipment moves into their isolated cove, and Johnny has his surfboard smashed by the remote controlled boat they claim to be testing. The youngsters are paid off and warned off, but why? Who is the sleezy [sic] Mr Luth? An explosion in the bay finally decides them, they will swim out at night and find out the answers.