Biggles get suspicious over a series of robberies that could only have been managed with air support. Suspecting a single gang is behind them all he seeks to infiltrate and then capture the gang in action.

The adventure wanders from England to Australia to Monte Carlo, before a climax in the gang's hideout in the african desert. With thanks to Bertie (going undercover) and Marcel (his first case with Biggles) the gang is captured and/or killed trying to escape.