Sea Witch Comes Home by Malcolm Saville
 
Why has Richard Channing disappeared in his boat Sea Witch, leaving his children Paul and Rose to fend for themselves? Is he mixed up in some dangerous business? Because Paul is desperately worried about his father he appeals for help to one of his school friends, David Morton, which is why David and the twins, Dickie and Mary, go to Walberswick and have an adventure in country that is new to them.
 
This tremendously exciting story takes us to the wind-swept sand dunes of East Anglia, where the North Sea hisses along lonely shingled beaches and slowly, relentlessly eats into the sandy cliffs. We are introduced to several new characters as the three Lone Piners, with their friends Paul and the delightful Rose, become deeply involved in some hair-raising events. The climax comes when, after a great storm, David rescues Rose from the raging waters just as the sea breaks through the coast defences, as it actually did in 1953.