Sheldon Lawrence is "Danny", an American freestyle swimmer who comes to Kent to to swim the English Channel - all 21 miles of it - over to France. He is trained by his determined brother "Griff" (John Ireland) and it's at one such training session they encounter "Kitty" (Joy Webster), also planning to make the trip - and so they decide to team up. She is sponsored by "Seymour" (Derek Bond), a married man with whom she is having an affair. She gives him an ultimatum before she sets off on her task, a pea soup fog sets in and next thing... "Danny" is sure foul play is involved and he sets out to... read the rest.