Jill, Robin and Bunkle de Salis are holidaying on the French Riviera when their mother is called away and their governess taken ill. After intercepting an SOS signal from an injured British Secret Service Agent they are charged with taking some top secret papers to their father who is also in the Intelligence Service. There follows a race across France and Switzerland, helped by Dick and Jean Fraser, who first appeared in The Far Island, and together they overcome all sorts of obstacles in their adventures as they race to Switzerland to deliver the secret documents. This is the first in the 'Bunkle' series about the de Salis family.