In 1940, the Royal Air Force fights a desperate battle against the might of the Luftwaffe for control of the skies over Britain, thus preventing the Nazi invasion of Britain.
Seeking revenge against the rival clan responsible for the killing, Hagbard, the son of a slain Norse king, calms down long enough to establish a truce. He also falls in love with Signe, the daughter of his one-time enemy. Signe's former beau, sizzling with jealousy, breaks the truce and makes it appear that Hagbard was responsible.
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.
