London, Sussex and Normandy all play a major part in tracking down the master-mind behind the large-scale robberies which have bedevilled Britain for the past year. Where does this super-crook hide his stolen property, and what useful purpose does a newly built brick building serve behind the high walls of Brindon Hall Park?

When the chase takes Biggles across the Channel, he is more than grateful to Marcel Brissac for turning up in the nick of time.